Fix windowed plugins not appearing if opened in the background until the browser resizes.

BUG=335900
R=ben@chromium.org

Review URL: https://codereview.chromium.org/150073002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247881 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247881