Regression - Flickering issues in blink

The regression came from making the style recalculations
compositor driven: when an <iframe> becomes composited,
the code triggers an extra style recalculation. In the
old code, it would happen as pat of the same frame but
in the new code, it would happen in a follow-up frame
causing the flickering issue.

The fix is to add an extra style recalc to cover the
previous case while making sure we don't allow more
cases to piggy back on this work-around.

Unfortunately no test as the flickering issue requires
us to dump the exact frame that was wrong, which is not
possible in our testing framework. I also couldn't turn
this into a unit test either.

BUG=332024

Review URL: https://codereview.chromium.org/232393002

git-svn-id: svn://svn.chromium.org/blink/trunk@171585 bbb929c8-8fbe-4397-9dbb-9b2b20218538