The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/973b7b9212b8d7b956d50f00792995d9712e4186

commit 973b7b9212b8d7b956d50f00792995d9712e4186
Author: Stephen Chenney <schenney@chromium.org>
Date: Fri Aug 04 15:24:55 2017

Fix border radius masks for transformed children.

A previous change starting using the compositing_bounds_ for
determining if a border radius clipping mask is required. However,
that bound does not include transformations that will be applied to
the child's layer. This change uses the child's layer bound in its
nearest clipping ancestor's space, and performs all clip testing in
that space.

Bug:  751798 
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I7e55c11cd54198dcfea2dc547e27133294465795
Reviewed-on: https://chromium-review.googlesource.com/539835
Commit-Queue: Stephen Chenney <schenney@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#492036}
[modify] https://crrev.com/973b7b9212b8d7b956d50f00792995d9712e4186/third_party/WebKit/LayoutTests/FlagExpectations/enable-slimming-paint-v2
[add] https://crrev.com/973b7b9212b8d7b956d50f00792995d9712e4186/third_party/WebKit/LayoutTests/compositing/composited-scaled-child-with-border-radius-parent-clip-expected.png
[add] https://crrev.com/973b7b9212b8d7b956d50f00792995d9712e4186/third_party/WebKit/LayoutTests/compositing/composited-scaled-child-with-border-radius-parent-clip-expected.txt
[add] https://crrev.com/973b7b9212b8d7b956d50f00792995d9712e4186/third_party/WebKit/LayoutTests/compositing/composited-scaled-child-with-border-radius-parent-clip.html
[add] https://crrev.com/973b7b9212b8d7b956d50f00792995d9712e4186/third_party/WebKit/LayoutTests/compositing/composited-translated-child-with-border-radius-parent-clip-expected.png
[add] https://crrev.com/973b7b9212b8d7b956d50f00792995d9712e4186/third_party/WebKit/LayoutTests/compositing/composited-translated-child-with-border-radius-parent-clip-expected.txt
[add] https://crrev.com/973b7b9212b8d7b956d50f00792995d9712e4186/third_party/WebKit/LayoutTests/compositing/composited-translated-child-with-border-radius-parent-clip.html
[modify] https://crrev.com/973b7b9212b8d7b956d50f00792995d9712e4186/third_party/WebKit/LayoutTests/compositing/layer-creation/overflow-scroll-overlap-expected.txt
[modify] https://crrev.com/973b7b9212b8d7b956d50f00792995d9712e4186/third_party/WebKit/LayoutTests/compositing/layer-creation/overflow-scroll-overlap.html
[modify] https://crrev.com/973b7b9212b8d7b956d50f00792995d9712e4186/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
[modify] https://crrev.com/973b7b9212b8d7b956d50f00792995d9712e4186/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h
[modify] https://crrev.com/973b7b9212b8d7b956d50f00792995d9712e4186/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMappingTest.cpp

Pls apply appropriate OSs label. Thank you.

This bug requires manual review: M61 has already been promoted to the beta branch, so this requires manual review
Please contact the milestone owner if you have questions.
Owners: amineer@(Android), cmasso@(iOS), ketakid@(ChromeOS), govind@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Approving merge to M61 Chrome OS.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ad8f597ed5da223d8d829db82f2d807ae6af97a0

commit ad8f597ed5da223d8d829db82f2d807ae6af97a0
Author: Stephen Chenney <schenney@chromium.org>
Date: Mon Aug 07 15:26:49 2017

Fix border radius masks for transformed children.

M-61 Merge.

A previous change starting using the compositing_bounds_ for
determining if a border radius clipping mask is required. However,
that bound does not include transformations that will be applied to
the child's layer. This change uses the child's layer bound in its
nearest clipping ancestor's space, and performs all clip testing in
that space.

TBR=schenney@chromium.org

(cherry picked from commit 973b7b9212b8d7b956d50f00792995d9712e4186)

Bug:  751798 
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I7e55c11cd54198dcfea2dc547e27133294465795
Reviewed-on: https://chromium-review.googlesource.com/539835
Commit-Queue: Stephen Chenney <schenney@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#492036}
Reviewed-on: https://chromium-review.googlesource.com/603967
Reviewed-by: Stephen Chenney <schenney@chromium.org>
Cr-Commit-Position: refs/branch-heads/3163@{#346}
Cr-Branched-From: ff259bab28b35d242e10186cd63af7ed404fae0d-refs/heads/master@{#488528}
[modify] https://crrev.com/ad8f597ed5da223d8d829db82f2d807ae6af97a0/third_party/WebKit/LayoutTests/FlagExpectations/enable-slimming-paint-v2
[add] https://crrev.com/ad8f597ed5da223d8d829db82f2d807ae6af97a0/third_party/WebKit/LayoutTests/compositing/composited-scaled-child-with-border-radius-parent-clip-expected.png
[add] https://crrev.com/ad8f597ed5da223d8d829db82f2d807ae6af97a0/third_party/WebKit/LayoutTests/compositing/composited-scaled-child-with-border-radius-parent-clip-expected.txt
[add] https://crrev.com/ad8f597ed5da223d8d829db82f2d807ae6af97a0/third_party/WebKit/LayoutTests/compositing/composited-scaled-child-with-border-radius-parent-clip.html
[add] https://crrev.com/ad8f597ed5da223d8d829db82f2d807ae6af97a0/third_party/WebKit/LayoutTests/compositing/composited-translated-child-with-border-radius-parent-clip-expected.png
[add] https://crrev.com/ad8f597ed5da223d8d829db82f2d807ae6af97a0/third_party/WebKit/LayoutTests/compositing/composited-translated-child-with-border-radius-parent-clip-expected.txt
[add] https://crrev.com/ad8f597ed5da223d8d829db82f2d807ae6af97a0/third_party/WebKit/LayoutTests/compositing/composited-translated-child-with-border-radius-parent-clip.html
[modify] https://crrev.com/ad8f597ed5da223d8d829db82f2d807ae6af97a0/third_party/WebKit/LayoutTests/compositing/layer-creation/overflow-scroll-overlap-expected.txt
[modify] https://crrev.com/ad8f597ed5da223d8d829db82f2d807ae6af97a0/third_party/WebKit/LayoutTests/compositing/layer-creation/overflow-scroll-overlap.html
[modify] https://crrev.com/ad8f597ed5da223d8d829db82f2d807ae6af97a0/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
[modify] https://crrev.com/ad8f597ed5da223d8d829db82f2d807ae6af97a0/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.h
[modify] https://crrev.com/ad8f597ed5da223d8d829db82f2d807ae6af97a0/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMappingTest.cpp

Android: Works as per expected behavior, Tested on Pixel XL / NJH47D. 
Issue verified on 61.0.3163.42.