simpleperf: use libbacktrace_offline static library.

Device may not have libbacktrace_offline shared library, so always
using libbacktrace_offline static library.
Use simpleperf namespace to avoid conflicts with ThreadEntry in
libbacktrace.

Bug: 28152982
Change-Id: Ia2cdbee3b28556c790ccd7b061a801ed96f9b97c
diff --git a/simpleperf/thread_tree.h b/simpleperf/thread_tree.h
index 3652bbc..de10138 100644
--- a/simpleperf/thread_tree.h
+++ b/simpleperf/thread_tree.h
@@ -25,6 +25,8 @@
 
 #include "dso.h"
 
+namespace simpleperf {
+
 struct MapEntry {
   uint64_t start_addr;
   uint64_t len;
@@ -97,6 +99,12 @@
   Symbol unknown_symbol_;
 };
 
+}  // namespace simpleperf
+
+using MapEntry = simpleperf::MapEntry;
+using ThreadEntry = simpleperf::ThreadEntry;
+using ThreadTree = simpleperf::ThreadTree;
+
 struct Record;
 
 void BuildThreadTree(const Record& record, ThreadTree* thread_tree);