Fix propagation of clip-path and border-radius clipping to child layers

Fix propagation of clip-path and border-radius clipping to child layers

RenderLayer clips of any shape other than a rectangle were not properly
propagated to child render layers, which is required for overflow
clipping and for CSS clip-path. This patch resolves the problem by
recursively applying clips that propagate from DOM ancestors
of the current render layer.

BUG=237100

[Justin Novosad, 2013-11-19 22:02:40]

PTAL

[Justin Novosad, 2013-11-20 00:27:42]

Reviewers: I just became aware of this other patch that is up for review. It has
an overlapping purpose: https://codereview.chromium.org/19954010/

[Justin Novosad, 2013-11-20 16:13:22]

On 2013/11/20 00:27:42, junov wrote:
> Reviewers: I just became aware of this other patch that is up for review. It
has
> an overlapping purpose: https://codereview.chromium.org/19954010/

Cancelling this review in favor of the other propsed CL