Fire resize events with requestAnimationFrame timing

Instead of spamming resize events when there are repeated layouts
that cause iframes to resize we can delay the event until raf timing
so that we only need to fire at most one per 16ms. This should reduce
the number of resize events dramatically on a page that is causing
synchronous layouts in JS that are making iframes change size.

R=ojan@chromium.org

Review URL: https://codereview.chromium.org/27430002

git-svn-id: svn://svn.chromium.org/blink/trunk@159766 bbb929c8-8fbe-4397-9dbb-9b2b20218538