gestures: fix ill-formed code

To resolve ambiguities during overload resolution, `using
V::operator()...;` is needed here in well-formed C++ code. Clang
incorrectly let this code pass without diagnostics before. See
discussion on https://reviews.llvm.org/D155387 for more details.

BUG=b:305745122
TEST=emerge-jacuzzi gestures

Change-Id: I96dc35d87a0289863adc847a158b62e6f22a655e
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/gestures/+/4944553
Code-Coverage: Zoss <zoss-cl-coverage@prod.google.com>
Tested-by: George Burgess <gbiv@chromium.org>
Reviewed-by: Sean O'Brien <seobrien@chromium.org>
Commit-Queue: George Burgess <gbiv@chromium.org>
1 file changed