Make URLRequestThrottlerEntryInterface inherit RefCountedThreadSafe,
as a quick fix for bug 64501. yzshen is planning to refactor these
classes significantly, so I won't make a bigger change at this point
(e.g. to prevent use of the interface on different threads).

BUG=64501
TEST=ThreadSanitizer complains no more.

Review URL: http://codereview.chromium.org/5364003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@67471 0039d316-1c4b-4281-b951-d872f2087c98
2 files changed