Update parent layout when child frame requests innerHeight/innerWidth.

The child frame dimensions may depend on the parent frame's layout. So
we need to update the parent frame's layout when the child asks for
innerHeight or innerWidth.

Without this patch, the test case incorrectly returns 0 for the
innerHeight/innerWidth queriers prior to the forced layout.

BUG=258175

Review URL: https://chromiumcodereview.appspot.com/19272007

git-svn-id: svn://svn.chromium.org/blink/trunk@154292 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Introduce toHTMLCanvasElement

To avoid direct use of static_cast, this patch introduces toHTMLCanvasElement for code cleanup.

Review URL: https://chromiumcodereview.appspot.com/19315005

git-svn-id: svn://svn.chromium.org/blink/trunk@154293 bbb929c8-8fbe-4397-9dbb-9b2b20218538