Fix browser theme provider cache miss crash.
Fix browser theme provider cache miss crash.

BUG=11717

Review URL: http://codereview.chromium.org/113225

git-svn-id: http://src.chromium.org/svn/trunk/src@15796 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 95d0f203eb5a291828e7d288b1e3a55b4cefdbad
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