Bypass cached element rects in AXLayoutObject.

Bypass cached element rects in AXLayoutObject.

AXLayoutObject has code to cache the computed bounding box of an element
because the computation can be expensive. However, it has a bug in that
the cache doesn't get properly invalidated when an object's position changes
due to only a CSS transformation.

This is resulting in a serious user issue on Android (b/28988142) so
this patch just temporarily removes the element rect caching. This will
unfortunately impact performance, some pages will load more slowly when
accessibility is enabled.

I've been working on a better longer-term fix for many months - storing
relative bounding boxes and transformation matrixes instead. It's much
faster to compute those and doesn't require any caching to be fast.
Unfortuantely it looks like we need to trade performance for correctness
in the short term because there isn't a trivial fix to make the cache
work.

BUG=629439
Committed: https://crrev.com/d091cc2097ed7cedb7d310a4161f022ae870bddc
Cr-Commit-Position: refs/heads/master@{#406663}

[dmazzoni, 2016-07-20 16:26:11]

The CQ bit was checked by dmazzoni@chromium.org to run a CQ dry run

[dmazzoni, 2016-07-20 16:26:33]

dmazzoni@chromium.org changed reviewers:
+ aboxhall@chromium.org, nektar@chromium.org

[commit-bot: I haz the power, 2016-07-20 16:26:37]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[aboxhall, 2016-07-20 16:30:11]

lgtm

https://codereview.chromium.org/2168663002/diff/1/third_party/WebKit/Source/m...
File third_party/WebKit/Source/modules/accessibility/AXLayoutObject.cpp (right):

https://codereview.chromium.org/2168663002/diff/1/third_party/WebKit/Source/m...
third_party/WebKit/Source/modules/accessibility/AXLayoutObject.cpp:205: return
computeElementRect();
Add a comment pointing to the bug tracking the longer-term fix?

[aboxhall, 2016-07-20 16:30:12]

lgtm

lgtm

[dmazzoni, 2016-07-20 17:24:16]

https://codereview.chromium.org/2168663002/diff/1/third_party/WebKit/Source/m...
File third_party/WebKit/Source/modules/accessibility/AXLayoutObject.cpp (right):

https://codereview.chromium.org/2168663002/diff/1/third_party/WebKit/Source/m...
third_party/WebKit/Source/modules/accessibility/AXLayoutObject.cpp:205: return
computeElementRect();
On 2016/07/20 at 16:30:11, aboxhall wrote:
> Add a comment pointing to the bug tracking the longer-term fix?

Sure, done.

[dmazzoni, 2016-07-20 17:24:20]

The CQ bit was checked by dmazzoni@chromium.org

[dmazzoni, 2016-07-20 17:24:21]

The patchset sent to the CQ was uploaded after l-g-t-m from
aboxhall@chromium.org
Link to the patchset: https://codereview.chromium.org/2168663002/#ps20001
(title: "Add link to bug")

[commit-bot: I haz the power, 2016-07-20 17:24:47]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-07-20 20:55:16]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-07-20 20:57:04]

Description was changed from

==========
Bypass cached element rects in AXLayoutObject.

AXLayoutObject has code to cache the computed bounding box of an element
because the computation can be expensive. However, it has a bug in that
the cache doesn't get properly invalidated when an object's position changes
due to only a CSS transformation.

This is resulting in a serious user issue on Android (b/28988142) so
this patch just temporarily removes the element rect caching. This will
unfortunately impact performance, some pages will load more slowly when
accessibility is enabled.

I've been working on a better longer-term fix for many months - storing
relative bounding boxes and transformation matrixes instead. It's much
faster to compute those and doesn't require any caching to be fast.
Unfortuantely it looks like we need to trade performance for correctness
in the short term because there isn't a trivial fix to make the cache
work.

BUG=629439
==========

to

==========
Bypass cached element rects in AXLayoutObject.

AXLayoutObject has code to cache the computed bounding box of an element
because the computation can be expensive. However, it has a bug in that
the cache doesn't get properly invalidated when an object's position changes
due to only a CSS transformation.

This is resulting in a serious user issue on Android (b/28988142) so
this patch just temporarily removes the element rect caching. This will
unfortunately impact performance, some pages will load more slowly when
accessibility is enabled.

I've been working on a better longer-term fix for many months - storing
relative bounding boxes and transformation matrixes instead. It's much
faster to compute those and doesn't require any caching to be fast.
Unfortuantely it looks like we need to trade performance for correctness
in the short term because there isn't a trivial fix to make the cache
work.

BUG=629439

Committed: https://crrev.com/d091cc2097ed7cedb7d310a4161f022ae870bddc
Cr-Commit-Position: refs/heads/master@{#406663}
==========

[commit-bot: I haz the power, 2016-07-20 20:57:05]

Patchset 2 (id:??) landed as
https://crrev.com/d091cc2097ed7cedb7d310a4161f022ae870bddc
Cr-Commit-Position: refs/heads/master@{#406663}