GitLab

google::Symbolize is not thread-safe since it manipulats a proc file
without locks.

This CL makes ProcessBacktrace thread-safe by base::Lock.

Bug: 904743

Change-Id: I12eb0f27158f39baa9683d74c98f4defdf0449f1
Reviewed-on: https://chromium-review.googlesource.com/c/1329814Reviewed-by: Taiju Tsuiki <tzik@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Commit-Queue: Hajime Hoshi <hajimehoshi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607937}