Fix Pepper plugins not painting in iframes. This will have to move back to RenderFrameImpl once the relevant callbacks are routed to the frame.

BUG=333824
R=nasko@chromium.org

Review URL: https://codereview.chromium.org/131083003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244723 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244723