[Mac] Prevent ppapi fullscreen window from dealloc while on stack.

If the rwhvm is being destroyed in response to a command accelerator,
the window being deallocated may still be executing code higher on the
stack.

BUG=154483


Review URL: https://chromiumcodereview.appspot.com/11416040

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@168463 0039d316-1c4b-4281-b951-d872f2087c98
2 files changed