Don't assert  if PostTask fails for WEBKIT thread, since it doesn't exist on single-process mode.  This asserts when the cache is cleared. Review URL: http://codereview.chromium.org/4165007
Don't assert  if PostTask fails for WEBKIT thread, since it doesn't exist on single-process mode.  This asserts when the cache is cleared.
Review URL: http://codereview.chromium.org/4165007

git-svn-id: http://src.chromium.org/svn/trunk/src@64318 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 79ae61b4ac89e7676267a4664a25f99dfd27cfad
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser