Fix clipping of squashed sibling layers with border radius masks

Fix clipping of squashed sibling layers with border radius masks

Merge to M-59 branch.

When a composited element with a border-radius overflow parent
has border radius and overflows itself, the element's clip rect
is included on the mask layer for the parent, which causes incorrect
clipping of sibling content.

Unfortunately a ref test fails due to a single pixel different on
the border radius.

TBR=chrishtr@chromium.org
BUG=709533
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2821733002
Cr-Original-Commit-Position: refs/heads/master@{#465028}
Review-Url: https://codereview.chromium.org/2826673003 .
Cr-Commit-Position: refs/branch-heads/3029@{#740}
Cr-Branched-From: 939b32ee5ba05c396eef3fd992822fcca9a2e262-refs/heads/master@{#454471}
Committed: https://chromium.googlesource.com/chromium/src/+/9334d38e3e4cc900a2987689269807ddc7bda09c

[Stephen Chennney, 2017-04-18 14:04:59]

Description was changed from

==========
Fix clipping of squashed sibling layers with border radius masks

Merge to M-59 branch.

When a composited element with a border-radius overflow parent
has border radius and overflows itself, the element's clip rect
is included on the mask layer for the parent, which causes incorrect
clipping of sibling content.

Unfortunately a ref test fails due to a single pixel different on
the border radius.

TBR=chrishtr@chromium.org
BUG=709533
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2821733002
Cr-Commit-Position: refs/heads/master@{#465028}
==========

to

==========
Fix clipping of squashed sibling layers with border radius masks

Merge to M-59 branch.

When a composited element with a border-radius overflow parent
has border radius and overflows itself, the element's clip rect
is included on the mask layer for the parent, which causes incorrect
clipping of sibling content.

Unfortunately a ref test fails due to a single pixel different on
the border radius.

TBR=chrishtr@chromium.org
BUG=709533
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Review-Url: https://codereview.chromium.org/2821733002
Cr-Original-Commit-Position: refs/heads/master@{#465028}
Review-Url: https://codereview.chromium.org/2826673003 .
Cr-Commit-Position: refs/branch-heads/3029@{#740}
Cr-Branched-From:
939b32ee5ba05c396eef3fd992822fcca9a2e262-refs/heads/master@{#454471}
Committed:
https://chromium.googlesource.com/chromium/src/+/9334d38e3e4cc900a29876892698...
==========

[Stephen Chennney, 2017-04-18 14:05:00]

Committed patchset #1 (id:1) manually as
9334d38e3e4cc900a2987689269807ddc7bda09c (presubmit successful).