Revert of Put the squashing layer underneath the ancestor clipping layer if present. (https://codereview.chromium.org/215823002/)

Reason for revert:
This appears to have unexpected effects on rendering. Bits of gmail are missing for example.

Original issue's description:
> Put the squashing layer underneath the ancestor clipping layer if present.
> 
> Previously, this was the case for m_graphicsLayer but not m_squashingLayer.
> Since they now are guaranteed to have the same clipping ancestor, this is both
> safe and correct.
> 
> BUG=336563
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=170348

TBR=hartmanng@chromium.org,chrishtr@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=336563

Review URL: https://codereview.chromium.org/218313002

git-svn-id: svn://svn.chromium.org/blink/trunk@170413 bbb929c8-8fbe-4397-9dbb-9b2b20218538