Suppress the races in base::Histogram::Add and base::HistogramSamples::Add
until https://codereview.chromium.org/116983004/ is landed.

BUG=46840
TBR=jar@chromium.org

Review URL: https://codereview.chromium.org/105903007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242521 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242521