Revert of Fix bugs in clip parent calculations (https://codereview.chromium.org/402283003/)

Reason for revert:
non-reparented-overlay-scrollbars.html fails on the following bots:

http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Mac10.7/builds/29607
http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Mac10.8/builds/27919
http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Mac10.8%20%28retina%29/builds/16557

Original issue's description:
> Fix bugs in clip parent calculations
> 
> I noticed two bugs in the clip parent code - when walking up the layers
> in the stacking tree looking for clipping layers, I'd forgotten to
> consider the layers themselves (I'd only considered their clipping
> containers). I'd also incorrectly gated promotion for having a clip
> parent on having an ancestor scrolling layer that needed composited
> scrolling. This condition was bogus: we often need a clip parent
> precisely because we have no ancestor scrolling layer (eg, we're fixed
> positioned and have 'escaped' our ancestor scrollers in tree order).
> 
> BUG=None
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=178649

TBR=abarth@chromium.org,vollick@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=None

Review URL: https://codereview.chromium.org/410683002

git-svn-id: svn://svn.chromium.org/blink/trunk@178665 bbb929c8-8fbe-4397-9dbb-9b2b20218538