Revert of Revert of Put the squashing layer underneath the ancestor clipping layer if present.

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
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=170507

[chrishtr, 2014-04-01 03:05:04]

Created Revert of Revert of Put the squashing layer underneath the ancestor
clipping layer if present.

[commit-bot: I haz the power, 2014-04-01 03:05:06]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/chrishtr@chromium.org/219223008/1

[commit-bot: I haz the power, 2014-04-01 03:05:34]

Change committed as 170507