Limit ScrollAnchor to 20 adjustments between user scrolls.

Limit ScrollAnchor to 20 adjustments between user scrolls.

This somewhat mitigates the impact of pathological feedback loops with scroll
event handlers.

BUG=601906
Committed: https://crrev.com/34ae0389f0c660c23f691595341188acc5444e00
Cr-Commit-Position: refs/heads/master@{#403491}

[skobes, 2016-07-01 00:10:03]

skobes@chromium.org changed reviewers:
+ ymalik@chromium.org

[ymalik, 2016-07-01 01:07:11]

lgtm with questions

https://codereview.chromium.org/2118683002/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/layout/ScrollAnchor.cpp (right):

https://codereview.chromium.org/2118683002/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/ScrollAnchor.cpp:17: static const int
kMaxAdjustments = 20;
How did you come up with this number? We do have some UMA metrics that may be
helpful in picking this. 

If I understand correctly, with this change, in the techcunch header bounce
case, we will now see it stop after bouncing for a little bit?

https://codereview.chromium.org/2118683002/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/ScrollAnchor.cpp:257: if
(++m_adjustmentCount <= kMaxAdjustments)
Brief comment explaining the rationale behind this?

[skobes, 2016-07-01 17:28:26]

https://codereview.chromium.org/2118683002/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/layout/ScrollAnchor.cpp (right):

https://codereview.chromium.org/2118683002/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/ScrollAnchor.cpp:17: static const int
kMaxAdjustments = 20;
On 2016/07/01 01:07:11, ymalik wrote:
> How did you come up with this number? We do have some UMA metrics that may be
> helpful in picking this. 
> 
> If I understand correctly, with this change, in the techcunch header bounce
> case, we will now see it stop after bouncing for a little bit?

I tried to pick something high enough to preserve adjustments when an ad
animates its expansion, but low enough that you don't have to wait a long time
to break out of the infinite loop case.  The video I posted to the bug shows
what it looks like.

https://codereview.chromium.org/2118683002/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/ScrollAnchor.cpp:257: if
(++m_adjustmentCount <= kMaxAdjustments)
On 2016/07/01 01:07:11, ymalik wrote:
> Brief comment explaining the rationale behind this?

Done.

[skobes, 2016-07-01 17:28:44]

The CQ bit was checked by skobes@chromium.org

[skobes, 2016-07-01 17:28:44]

The patchset sent to the CQ was uploaded after l-g-t-m from ymalik@chromium.org
Link to the patchset: https://codereview.chromium.org/2118683002/#ps20001
(title: "add comment")

[commit-bot: I haz the power, 2016-07-01 17:29:05]

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, 2016-07-01 18:49:35]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-07-01 18:51:56]

Description was changed from

==========
Limit ScrollAnchor to 20 adjustments between user scrolls.

This somewhat mitigates the impact of pathological feedback loops with scroll
event handlers.

BUG=601906
==========

to

==========
Limit ScrollAnchor to 20 adjustments between user scrolls.

This somewhat mitigates the impact of pathological feedback loops with scroll
event handlers.

BUG=601906

Committed: https://crrev.com/34ae0389f0c660c23f691595341188acc5444e00
Cr-Commit-Position: refs/heads/master@{#403491}
==========

[commit-bot: I haz the power, 2016-07-01 18:51:57]

Patchset 2 (id:??) landed as
https://crrev.com/34ae0389f0c660c23f691595341188acc5444e00
Cr-Commit-Position: refs/heads/master@{#403491}