Suppress races on _M_refcount between _M_dispose() and _M_is_leaked().

BUG=181502

Review URL: https://codereview.chromium.org/14322012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@194566 0039d316-1c4b-4281-b951-d872f2087c98

tools/valgrind/tsan_v2/suppressions.txt

@@ -44,6 +44,7 @@ race:third_party/libvpx/source/libvpx/vp8/encoder/*
 
 # See http://crbug.com/181502
 race:_M_rep
+race:_M_is_leaked
 
 # http://crbug.com/189177
 race:thread_manager