GitLab

So avoid crashing even if the destructor is not
called before killing the IO thread.

BUG=49271
TEST=none


Review URL: http://codereview.chromium.org/3044006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@52924 0039d316-1c4b-4281-b951-d872f2087c98