Check for context changes during Mac plugin event handling.
Check for context changes during Mac plugin event handling.

Ensure that we don't use a context that's no longer valid

BUG=32773
TEST=Toggle YouTube videos between normal and expanded size.

Review URL: http://codereview.chromium.org/555038

git-svn-id: http://src.chromium.org/svn/trunk/src@36792 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 6123c11f7eefdb01d082aafad8d95600dd493c3a
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