Suppress a race in base::Thread::StopSoon()

BUG=258935
TBR=jam@chromium.org

Review URL: https://codereview.chromium.org/1063973003

Cr-Original-Commit-Position: refs/heads/master@{#326267}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 4e93bf078122f5221eba86b8acfc696f371ccacd

sanitizers/tsan_suppressions.cc

@@ -122,6 +122,9 @@ char kTSanDefaultSuppressions[] =
 "race:base::PowerMonitor::RemoveObserver\n"
 "race:base::PowerMonitor::IsOnBatteryPower\n"
 
+// http://crbug.com/258935
+"race:base::Thread::StopSoon\n"
+
 // http://crbug.com/268941
 "race:tracked_objects::ThreadData::tls_index_\n"