Add an accessibility role for the iframe element (re-land).

We can add a layout test after adding TestRunner support on the Chromium side,
or we could just test it in Chromium.

BUG=347464

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=168156

Review URL: https://codereview.chromium.org/183183005

git-svn-id: svn://svn.chromium.org/blink/trunk@170426 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Optimize repaint on FrameView resize

Previously we always repaint the full FrameView on resize.

Don't mark full repaint if the resize is height-only and writing mode
is horizontal. Any descendants needing repaint because of FrameView
resize will still schedule their own repaints.

BUG=258219
TEST=WebFrameTest.sizeChangeRepaint

Review URL: https://codereview.chromium.org/213103003

git-svn-id: svn://svn.chromium.org/blink/trunk@170427 bbb929c8-8fbe-4397-9dbb-9b2b20218538