Replace google::protobuf::string with std::string.

google::protobuf::string has been removed in recent releases of
Protocol Buffers library.

Bug: 203713560
Test: OUT_DIR=out prebuilts/clang-tools/build-prebuilts.sh
Change-Id: I813648da19aa6e892a81a3f326cd42257f162657
diff --git a/kythe/cxx/common/kythe_metadata_file.cc b/kythe/cxx/common/kythe_metadata_file.cc
index 3d2536e..3f82c6e 100644
--- a/kythe/cxx/common/kythe_metadata_file.cc
+++ b/kythe/cxx/common/kythe_metadata_file.cc
@@ -46,7 +46,7 @@
 absl::optional<std::string> LoadCommentMetadata(absl::string_view buf_string,
                                                 size_t comment_slash_pos,
                                                 size_t data_start_pos) {
-  google::protobuf::string raw_data;
+  std::string raw_data;
   // Over-reserves--though we expect the comment to be the only thing in the
   // file or the last thing in the file, so this approximation is reasonable.
   raw_data.reserve(buf_string.size() - comment_slash_pos);
@@ -74,9 +74,9 @@
     }
     break;
   }
-  google::protobuf::string decoded;
+  std::string decoded;
   return absl::Base64Unescape(raw_data, &decoded)
-             ? absl::optional<std::string>(std::string(decoded))
+             ? absl::optional<std::string>(decoded)
              : absl::nullopt;
 }
 
diff --git a/kythe/cxx/extractor/testdata/claim_pragma_test.cc b/kythe/cxx/extractor/testdata/claim_pragma_test.cc
index 077ec4f..97dc9f8 100644
--- a/kythe/cxx/extractor/testdata/claim_pragma_test.cc
+++ b/kythe/cxx/extractor/testdata/claim_pragma_test.cc
@@ -22,8 +22,6 @@
 using ::google::protobuf::util::MessageDifferencer;
 using ::testing::ElementsAre;
 
-using pbstring = ::google::protobuf::string;
-
 constexpr char kExpectedContents[] = R"(
 v_name {
   language: "c++"
@@ -113,7 +111,7 @@
 //                                {"message", "inner", "field"});
 const FieldDescriptor* FindNestedFieldByLowercasePath(
     const google::protobuf::Descriptor* descriptor,
-    const std::vector<pbstring>& field_names) {
+    const std::vector<std::string>& field_names) {
   const FieldDescriptor* field = nullptr;
   for (const auto& name : field_names) {
     if (descriptor == nullptr) return nullptr;
@@ -147,7 +145,7 @@
   }
 
  private:
-  using HashMap = std::unordered_map<pbstring, size_t>;
+  using HashMap = std::unordered_map<std::string, size_t>;
 
   ComparisonResult Compare(
       const Message& message_1, const Message& message_2,
@@ -163,8 +161,8 @@
     if (field->is_repeated()) {
       // Allocate scratch strings to store the result if a conversion is
       // needed.
-      pbstring scratch1;
-      pbstring scratch2;
+      std::string scratch1;
+      std::string scratch2;
       return CompareCanonicalHash(reflection_1->GetRepeatedStringReference(
                                       message_1, field, index_1, &scratch1),
                                   reflection_2->GetRepeatedStringReference(
@@ -172,23 +170,23 @@
     } else {
       // Allocate scratch strings to store the result if a conversion is
       // needed.
-      pbstring scratch1;
-      pbstring scratch2;
+      std::string scratch1;
+      std::string scratch2;
       return CompareCanonicalHash(
           reflection_1->GetStringReference(message_1, field, &scratch1),
           reflection_2->GetStringReference(message_2, field, &scratch2));
     }
   }
 
-  ComparisonResult CompareCanonicalHash(const pbstring& string_1,
-                                        const pbstring& string_2) {
+  ComparisonResult CompareCanonicalHash(const std::string& string_1,
+                                        const std::string& string_2) {
     return HashIndex(&left_message_hashes_, string_1) ==
                    HashIndex(&right_message_hashes_, string_2)
                ? SAME
                : DIFFERENT;
   }
 
-  static size_t HashIndex(HashMap* canonical_map, const pbstring& hash) {
+  static size_t HashIndex(HashMap* canonical_map, const std::string& hash) {
     size_t index = canonical_map->size();
     // We use an index equivalent to the visitation order of the hashes.
     // This is potentially fragile as we really only care if a protocol buffer
@@ -231,7 +229,7 @@
 
     kythe::proto::CompilationUnit expected;
     ASSERT_TRUE(TextFormat::ParseFromString(kExpectedContents, &expected));
-    google::protobuf::string diffs;
+    std::string diffs;
     diff.ReportDifferencesToString(&diffs);
     EXPECT_TRUE(diff.Compare(expected, unit)) << diffs;
 
diff --git a/kythe/cxx/indexer/cxx/KytheIndexerUnitTest.cc b/kythe/cxx/indexer/cxx/KytheIndexerUnitTest.cc
index ca87642..d2807ea 100644
--- a/kythe/cxx/indexer/cxx/KytheIndexerUnitTest.cc
+++ b/kythe/cxx/indexer/cxx/KytheIndexerUnitTest.cc
@@ -277,9 +277,9 @@
   EXPECT_EQ(vname_target.DebugString(), entry.target().DebugString());
 }
 
-static void WriteStringToStackAndBuffer(const google::protobuf::string& value,
+static void WriteStringToStackAndBuffer(const std::string& value,
                                         kythe::BufferStack* stack,
-                                        google::protobuf::string* buffer) {
+                                        std::string* buffer) {
   unsigned char* bytes = stack->WriteToTop(value.size());
   memcpy(bytes, value.data(), value.size());
   if (buffer) {
@@ -289,7 +289,7 @@
 
 TEST(KytheIndexerUnitTest, BufferStackWrite) {
   kythe::BufferStack stack;
-  google::protobuf::string expected, actual;
+  std::string expected, actual;
   {
     google::protobuf::io::StringOutputStream stream(&actual);
     stack.Push(0);
@@ -305,7 +305,7 @@
 
 TEST(KytheIndexerUnitTest, BufferStackMergeDown) {
   kythe::BufferStack stack;
-  google::protobuf::string actual;
+  std::string actual;
   {
     google::protobuf::io::StringOutputStream stream(&actual);
     stack.Push(0);
@@ -344,7 +344,7 @@
 
 TEST(KytheIndexerUnitTest, BufferStackMergeFailures) {
   kythe::BufferStack stack;
-  google::protobuf::string actual;
+  std::string actual;
   {
     google::protobuf::io::StringOutputStream stream(&actual);
     ASSERT_FALSE(stack.MergeDownIfTooSmall(0, 2048));  // too few on the stack
diff --git a/kythe/cxx/indexer/cxx/proto_conversions.h b/kythe/cxx/indexer/cxx/proto_conversions.h
index 59e0ab1..7167093 100644
--- a/kythe/cxx/indexer/cxx/proto_conversions.h
+++ b/kythe/cxx/indexer/cxx/proto_conversions.h
@@ -25,7 +25,7 @@
 /// \brief Wrap a protobuf string in a StringRef.
 /// \param string The string to wrap.
 /// \return The wrapped string (which should not outlive `string`).
-inline llvm::StringRef ToStringRef(const google::protobuf::string& string) {
+inline llvm::StringRef ToStringRef(const std::string& string) {
   return llvm::StringRef(string.c_str(), string.size());
 }
 }  // namespace kythe
diff --git a/kythe/cxx/verifier/verifier.cc b/kythe/cxx/verifier/verifier.cc
index 1d05b7c..8f253ac 100644
--- a/kythe/cxx/verifier/verifier.cc
+++ b/kythe/cxx/verifier/verifier.cc
@@ -1288,7 +1288,7 @@
 }
 
 AstNode* Verifier::ConvertCodeFact(const yy::location& loc,
-                                   const google::protobuf::string& code_data) {
+                                   const std::string& code_data) {
   proto::common::MarkedSource marked_source;
   if (!marked_source.ParseFromString(code_data)) {
     std::cerr << loc << ": can't parse code protobuf" << std::endl;
diff --git a/kythe/cxx/verifier/verifier.h b/kythe/cxx/verifier/verifier.h
index 212dd1e..4db76b4 100644
--- a/kythe/cxx/verifier/verifier.h
+++ b/kythe/cxx/verifier/verifier.h
@@ -208,7 +208,7 @@
   /// \return null if something went wrong; otherwise, an AstNode corresponding
   /// to a VName of a synthetic node for `code_data`.
   AstNode* ConvertCodeFact(const yy::location& loc,
-                           const google::protobuf::string& code_data);
+                           const std::string& code_data);
 
   /// \brief Converts a MarkedSource message to a form that's useful
   /// to the verifier.
diff --git a/kythe/cxx/verifier/verifier_unit_test.cc b/kythe/cxx/verifier/verifier_unit_test.cc
index c530008..20c7f3f 100644
--- a/kythe/cxx/verifier/verifier_unit_test.cc
+++ b/kythe/cxx/verifier/verifier_unit_test.cc
@@ -2652,10 +2652,10 @@
 TEST(VerifierUnitTest, DontConvertMarkedSource) {
   Verifier v;
   MarkedSource source;
-  google::protobuf::string source_string;
+  std::string source_string;
   ASSERT_TRUE(source.SerializeToString(&source_string));
   google::protobuf::TextFormat::FieldValuePrinter printer;
-  google::protobuf::string enc_source = printer.PrintBytes(source_string);
+  std::string enc_source = printer.PrintBytes(source_string);
   ASSERT_TRUE(v.LoadInlineProtoFile(R"(
   entries {
     source { signature:"test" }
@@ -2673,10 +2673,10 @@
   Verifier v;
   v.ConvertMarkedSource();
   MarkedSource source;
-  google::protobuf::string source_string;
+  std::string source_string;
   ASSERT_TRUE(source.SerializeToString(&source_string));
   google::protobuf::TextFormat::FieldValuePrinter printer;
-  google::protobuf::string enc_source = printer.PrintBytes(source_string);
+  std::string enc_source = printer.PrintBytes(source_string);
   ASSERT_TRUE(v.LoadInlineProtoFile(R"(
   entries {
     source { signature:"test" }
@@ -2708,10 +2708,10 @@
     v.ConvertMarkedSource();
     MarkedSource source;
     source.set_kind(kind_enum);
-    google::protobuf::string source_string;
+    std::string source_string;
     ASSERT_TRUE(source.SerializeToString(&source_string));
     google::protobuf::TextFormat::FieldValuePrinter printer;
-    google::protobuf::string enc_source = printer.PrintBytes(source_string);
+    std::string enc_source = printer.PrintBytes(source_string);
     ASSERT_TRUE(v.LoadInlineProtoFile(R"(
     entries {
       source { signature:"test" }
@@ -2732,10 +2732,10 @@
   v.ConvertMarkedSource();
   MarkedSource source;
   source.add_link()->add_definition("kythe://corpus#sig");
-  google::protobuf::string source_string;
+  std::string source_string;
   ASSERT_TRUE(source.SerializeToString(&source_string));
   google::protobuf::TextFormat::FieldValuePrinter printer;
-  google::protobuf::string enc_source = printer.PrintBytes(source_string);
+  std::string enc_source = printer.PrintBytes(source_string);
   ASSERT_TRUE(v.LoadInlineProtoFile(R"(
   entries {
     source { signature:"test" }
@@ -2754,10 +2754,10 @@
   v.ConvertMarkedSource();
   MarkedSource source;
   source.add_link()->add_definition("kythe:/&bad");
-  google::protobuf::string source_string;
+  std::string source_string;
   ASSERT_TRUE(source.SerializeToString(&source_string));
   google::protobuf::TextFormat::FieldValuePrinter printer;
-  google::protobuf::string enc_source = printer.PrintBytes(source_string);
+  std::string enc_source = printer.PrintBytes(source_string);
   ASSERT_FALSE(v.LoadInlineProtoFile(R"(
   entries {
     source { signature:"test" }
@@ -2772,10 +2772,10 @@
   v.ConvertMarkedSource();
   MarkedSource source;
   source.add_link();
-  google::protobuf::string source_string;
+  std::string source_string;
   ASSERT_TRUE(source.SerializeToString(&source_string));
   google::protobuf::TextFormat::FieldValuePrinter printer;
-  google::protobuf::string enc_source = printer.PrintBytes(source_string);
+  std::string enc_source = printer.PrintBytes(source_string);
   ASSERT_FALSE(v.LoadInlineProtoFile(R"(
   entries {
     source { signature:"test" }
@@ -2792,10 +2792,10 @@
   auto* link = source.add_link();
   link->add_definition("kythe://corpus#sig");
   link->add_definition("kythe://corpus#sig2");
-  google::protobuf::string source_string;
+  std::string source_string;
   ASSERT_TRUE(source.SerializeToString(&source_string));
   google::protobuf::TextFormat::FieldValuePrinter printer;
-  google::protobuf::string enc_source = printer.PrintBytes(source_string);
+  std::string enc_source = printer.PrintBytes(source_string);
   ASSERT_FALSE(v.LoadInlineProtoFile(R"(
   entries {
     source { signature:"test" }
@@ -2813,10 +2813,10 @@
   child->set_kind(MarkedSource::IDENTIFIER);
   child = source.add_child();
   child->set_kind(MarkedSource::CONTEXT);
-  google::protobuf::string source_string;
+  std::string source_string;
   ASSERT_TRUE(source.SerializeToString(&source_string));
   google::protobuf::TextFormat::FieldValuePrinter printer;
-  google::protobuf::string enc_source = printer.PrintBytes(source_string);
+  std::string enc_source = printer.PrintBytes(source_string);
   ASSERT_TRUE(v.LoadInlineProtoFile(R"(
   entries {
     source { signature:"test" }
@@ -2841,10 +2841,10 @@
   auto* link = child->add_link();
   link->add_definition("kythe://corpus#sig");
   link->add_definition("kythe://corpus#sig2");
-  google::protobuf::string source_string;
+  std::string source_string;
   ASSERT_TRUE(parent.SerializeToString(&source_string));
   google::protobuf::TextFormat::FieldValuePrinter printer;
-  google::protobuf::string enc_source = printer.PrintBytes(source_string);
+  std::string enc_source = printer.PrintBytes(source_string);
   ASSERT_FALSE(v.LoadInlineProtoFile(R"(
   entries {
     source { signature:"test" }
@@ -2864,10 +2864,10 @@
   source.set_lookup_index(42);
   source.set_default_children_count(43);
   source.set_add_final_list_token(true);
-  google::protobuf::string source_string;
+  std::string source_string;
   ASSERT_TRUE(source.SerializeToString(&source_string));
   google::protobuf::TextFormat::FieldValuePrinter printer;
-  google::protobuf::string enc_source = printer.PrintBytes(source_string);
+  std::string enc_source = printer.PrintBytes(source_string);
   ASSERT_TRUE(v.LoadInlineProtoFile(R"(
   entries {
     source { signature:"test" }
@@ -2890,10 +2890,10 @@
   Verifier v;
   MarkedSource source;
   v.IgnoreDuplicateFacts();
-  google::protobuf::string source_string;
+  std::string source_string;
   ASSERT_TRUE(source.SerializeToString(&source_string));
   google::protobuf::TextFormat::FieldValuePrinter printer;
-  google::protobuf::string enc_source = printer.PrintBytes(source_string);
+  std::string enc_source = printer.PrintBytes(source_string);
   ASSERT_TRUE(v.LoadInlineProtoFile(R"(
   entries {
     source { signature:"test" }
@@ -2914,10 +2914,10 @@
   Verifier v;
   v.ConvertMarkedSource();
   MarkedSource source;
-  google::protobuf::string source_string;
+  std::string source_string;
   ASSERT_TRUE(source.SerializeToString(&source_string));
   google::protobuf::TextFormat::FieldValuePrinter printer;
-  google::protobuf::string enc_source = printer.PrintBytes(source_string);
+  std::string enc_source = printer.PrintBytes(source_string);
   ASSERT_TRUE(v.LoadInlineProtoFile(R"(
   entries {
     source { signature:"test" }