Fix SafeAdd and SafeMultiply

BUG=145648,145544


Review URL: https://chromiumcodereview.appspot.com/10916165

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@155478 0039d316-1c4b-4281-b951-d872f2087c98
  size_t estimated_size() const {
    return memory_tracker_.GetMemRepresented();
  }

  size_t estimated_size() const {
    return memory_tracker_.GetMemRepresented();
  }
