Reinstate race suppression between AccumulateAndClearImplThreadStats and RasterTaskImpl::Raster()

The attempted fix only locked one side of the race, which isn't effective.

BUG=370244
TBR=ernstm@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/297493002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@271451 0039d316-1c4b-4281-b951-d872f2087c98

tools/valgrind/tsan_v2/suppressions.txt

@@ -254,6 +254,9 @@ race:WTF::Latin1Encoding()::globalLatin1Encoding
 # https://code.google.com/p/v8/issues/detail?id=3143
 race:v8::internal::FLAG_track_double_fields
 
+# http://crbug.com/370244
+race:cc::RenderingStatsInstrumentation::AccumulateAndClearImplThreadStats
+
 # https://crbug.com/369257
 # TODO(mtklein): annotate properly and remove suppressions.
 race:SandboxIPCHandler::HandleFontMatchRequest