Remove sync resize event from FrameView::setFrameRect.

This fixes a hang with resize events and seamless iframes that's
showing up on codereview.chromium.org with the rietveld usability
extension installed.

r156320 added this in a patch that was supposed to just be a refactor.
I'm not convinced we want this code. WebKit added it in
http://trac.webkit.org/changeset/149287 and
http://trac.webkit.org/changeset/150011 and updated it to work for
frame flattening (but not seamless!) in
http://trac.webkit.org/changeset/153640.

I don't really understand the changes to fast/forms, but they're just
undoing unexplained changes from r156320.

BUG=282603

Review URL: https://codereview.chromium.org/25092012

git-svn-id: svn://svn.chromium.org/blink/trunk@158578 bbb929c8-8fbe-4397-9dbb-9b2b20218538