Revert of Revert of Put the squashing layer underneath the ancestor clipping layer if present. (https://codereview.chromium.org/218313002/)

Reason for revert:
The breakage is only with --enable-universal-accelerated-overflow-scroll true. Since that feature is not launched and not tied to squashing, going to re-lad the original CL.

Original issue's description:
> 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
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=170413

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

Review URL: https://codereview.chromium.org/219223008

git-svn-id: svn://svn.chromium.org/blink/trunk@170507 bbb929c8-8fbe-4397-9dbb-9b2b20218538