Fix for cast extension pop-up is all blank.

For extensions, WebViewImpl runs in AutoResizeMode so resize()
is never called so the pinch viewport's compositing layers never
got their bounds set. When masks_to_bounds was turned on the
extensions were masked out by their empty-sized clipping layers.

This fix sets the pinch viewport size explicitly from the
layoutUpdated callback in the case of AutoResizeMode.

BUG=369331

Review URL: https://codereview.chromium.org/268593012

git-svn-id: svn://svn.chromium.org/blink/trunk@173238 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Auto-rebaseline for r173153

http://src.chromium.org/viewvc/blink?view=revision&revision=173153

BUG=368518
TBR=enne@chromium.org

Review URL: https://codereview.chromium.org/263993002

git-svn-id: svn://svn.chromium.org/blink/trunk@173239 bbb929c8-8fbe-4397-9dbb-9b2b20218538