Delete scrollCompensationAdjustment.

Delete scrollCompensationAdjustment.

This feature was added to compensate for fixed-position layers getting
positioned at integer positions but counterscrolled by a full,
fractional amount.  It wound up getting unused because it caused a
performance regression due to defeating the "aborted commit"
optimization during scrolling (every scroll increment with a fractional
change would cause a commit).

There are two ways we can move forward with main-thread fractional
scroll support from here, either 1) have CC automatically compute the
fractional part on the impl thread, or 2) change Blink so that
fixed-position elements don't include the scroll offset in their layout
position at all.  Either way, this scroll compensation feature is dead
code, so we can delete it now.

BUG=414283
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Committed: https://crrev.com/a9aad960d0bf105c2153a517cedcc57e4d53b0b5
Cr-Commit-Position: refs/heads/master@{#381180}

[aelias_OOO_until_Jul13, 2015-10-06 07:11:19]

aelias@chromium.org changed reviewers:
+ miletus@chromium.org, vollick@chromium.org

[aelias_OOO_until_Jul13, 2015-10-06 07:16:28]

aelias@chromium.org changed reviewers:
+ rbyers@chromium.org

[aelias_OOO_until_Jul13, 2015-10-06 07:37:06]

PTAL, this is another post-Blink-merge small cleanup I wanted to do.

vollick@, please take a look at the property tree change.  I *think* the scroll
snap correction is actually needed regardless of scroll compensation adjustment
per se, even though at an initial glance
https://codereview.chromium.org/1021823006 they seemed tied together.

[Yufeng Shen (Slow to review), 2015-10-06 15:09:27]

On 2015/10/06 07:37:06, aelias wrote:
> PTAL, this is another post-Blink-merge small cleanup I wanted to do.
> 
> vollick@, please take a look at the property tree change.  I *think* the
scroll
> snap correction is actually needed regardless of scroll compensation
adjustment
> per se, even though at an initial glance
> https://codereview.chromium.org/1021823006 they seemed tied together.

non-property-tree related part lgtm.

[Rick Byers, 2015-10-06 17:02:39]

WebKit/ LGTM

I'd still like to understand the plan for setting fractional scrollTop values
for high-dpi impl-thread scrolling (http://crbug.com/456622).  That's still
really important IMHO.

[aelias_OOO_until_Jul13, 2016-03-10 06:02:03]

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

[commit-bot: I haz the power, 2016-03-10 06:02:18]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1385123003/60001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1385123003/60001

[aelias_OOO_until_Jul13, 2016-03-10 06:05:25]

Very delayed PTAL.  vollick@, could you review the changes in cc/?

(I started looking at the fractional scroll code again today and realized I had
forgotten all about this pending patch after not getting the final cc/ review. 
This cleanup is still a good idea to do a few months later.)

[commit-bot: I haz the power, 2016-03-10 06:41:13]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-03-10 06:41:14]

Dry run: Try jobs failed on following builders:
  win_chromium_x64_rel_ng on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[Ian Vollick, 2016-03-13 16:59:44]

On 2016/03/10 06:41:14, commit-bot: I haz the power wrote:
> Dry run: Try jobs failed on following builders:
>   win_chromium_x64_rel_ng on tryserver.chromium.win (JOB_FAILED,
>
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

lgtm! This is fantastic.

[aelias_OOO_until_Jul13, 2016-03-14 18:21:26]

The CQ bit was checked by aelias@chromium.org

[aelias_OOO_until_Jul13, 2016-03-14 18:21:26]

The patchset sent to the CQ was uploaded after l-g-t-m from
miletus@chromium.org, rbyers@chromium.org
Link to the patchset: https://codereview.chromium.org/1385123003/#ps60001
(title: "Rebase to master")

[commit-bot: I haz the power, 2016-03-14 18:21:44]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1385123003/60001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1385123003/60001

[commit-bot: I haz the power, 2016-03-14 18:24:23]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-03-14 18:24:24]

Try jobs failed on following builders:
  ios_dbg_simulator_ninja on tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_dbg_simulator...)
  ios_rel_device_gn on tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device_gn...)
  ios_rel_device_ninja on tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device_ni...)

[aelias_OOO_until_Jul13, 2016-03-15 01:06:40]

The CQ bit was checked by aelias@chromium.org

[aelias_OOO_until_Jul13, 2016-03-15 01:06:40]

The patchset sent to the CQ was uploaded after l-g-t-m from
vollick@chromium.org, miletus@chromium.org, rbyers@chromium.org
Link to the patchset: https://codereview.chromium.org/1385123003/#ps80001
(title: "Rebase again")

[commit-bot: I haz the power, 2016-03-15 01:06:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1385123003/80001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1385123003/80001

[commit-bot: I haz the power, 2016-03-15 02:24:22]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-03-15 02:24:23]

Try jobs failed on following builders:
  linux_blink_rel on tryserver.blink (JOB_FAILED,
http://build.chromium.org/p/tryserver.blink/builders/linux_blink_rel/builds/8...)

[aelias_OOO_until_Jul13, 2016-03-15 04:36:33]

The CQ bit was checked by aelias@chromium.org

[commit-bot: I haz the power, 2016-03-15 04:36:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1385123003/80001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1385123003/80001

[commit-bot: I haz the power, 2016-03-15 05:10:40]

Committed patchset #5 (id:80001)

[commit-bot: I haz the power, 2016-03-15 05:11:51]

Description was changed from

==========
Delete scrollCompensationAdjustment.

This feature was added to compensate for fixed-position layers getting
positioned at integer positions but counterscrolled by a full,
fractional amount.  It wound up getting unused because it caused a
performance regression due to defeating the "aborted commit"
optimization during scrolling (every scroll increment with a fractional
change would cause a commit).

There are two ways we can move forward with main-thread fractional
scroll support from here, either 1) have CC automatically compute the
fractional part on the impl thread, or 2) change Blink so that
fixed-position elements don't include the scroll offset in their layout
position at all.  Either way, this scroll compensation feature is dead
code, so we can delete it now.

BUG=414283
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
==========

to

==========
Delete scrollCompensationAdjustment.

This feature was added to compensate for fixed-position layers getting
positioned at integer positions but counterscrolled by a full,
fractional amount.  It wound up getting unused because it caused a
performance regression due to defeating the "aborted commit"
optimization during scrolling (every scroll increment with a fractional
change would cause a commit).

There are two ways we can move forward with main-thread fractional
scroll support from here, either 1) have CC automatically compute the
fractional part on the impl thread, or 2) change Blink so that
fixed-position elements don't include the scroll offset in their layout
position at all.  Either way, this scroll compensation feature is dead
code, so we can delete it now.

BUG=414283
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Committed: https://crrev.com/a9aad960d0bf105c2153a517cedcc57e4d53b0b5
Cr-Commit-Position: refs/heads/master@{#381180}
==========

[commit-bot: I haz the power, 2016-03-15 05:11:52]

Patchset 5 (id:??) landed as
https://crrev.com/a9aad960d0bf105c2153a517cedcc57e4d53b0b5
Cr-Commit-Position: refs/heads/master@{#381180}