Round the scroll offset synced back to main instead of flooring.

Round the scroll offset synced back to main instead of flooring.

When scrolling up, flooring the scroll delta sent back to main can result
in main thinking that we have scrolled up by a pixel while cc still positions
layers as if we are at the old scroll position. To be technically correct
according to the frame that will be produced, we would need to round according
to the current scroll snap size but this isn ot easily known at the time of
rounding so we use the nearest integer since this is the common case.

BUG=663291
TEST=LayerTreeHostImplTest.SyncSubpixelScrollDelta
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel

Committed: https://crrev.com/75a7e4cb1ec29ded2e52539259233356caa883c8
Cr-Commit-Position: refs/heads/master@{#434022}

[flackr, 2016-11-16 19:05:35]

Description was changed from

==========
Round the scroll offset synced back to main instead of flooring.

When scrolling up, flooring the scroll delta sent back to main can result
in main thinking that we have scrolled up by a pixel while cc still positions
layers as if we are at the old scroll position. To be technically correct
according to the frame that will be produced, we would need to round according
to the current scroll snap size but this isn ot easily known at the time of
rounding so we use the nearest integer since this is the common case.

BUG=663291
TEST=LayerTreeHostImplTest.SyncSubpixelScrollDelta
==========

to

==========
Round the scroll offset synced back to main instead of flooring.

When scrolling up, flooring the scroll delta sent back to main can result
in main thinking that we have scrolled up by a pixel while cc still positions
layers as if we are at the old scroll position. To be technically correct
according to the frame that will be produced, we would need to round according
to the current scroll snap size but this isn ot easily known at the time of
rounding so we use the nearest integer since this is the common case.

BUG=663291
TEST=LayerTreeHostImplTest.SyncSubpixelScrollDelta
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel
==========

[flackr, 2016-11-16 19:32:28]

flackr@chromium.org changed reviewers:
+ weiliangc@chromium.org

[flackr, 2016-11-16 19:32:29]

Hey,

Can you take a look at this change? Currently when we're scrolling up by small
amounts cc tells blink that we have scrolled up a pixel even though it will
still snap to the old offset. This leads to jittering of fixed position elements
drawn on main which are also inconsistently positioned w.r.t. composited fixed
position elements.

Thanks!

[weiliangc, 2016-11-17 19:51:19]

LGTM.

(Sorry it took so long, I was worried cc used floor somewhere else that could be
affected by this but I don't think that's the case)

[flackr, 2016-11-17 20:03:07]

The CQ bit was checked by flackr@chromium.org

[commit-bot: I haz the power, 2016-11-17 20:04:52]

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, 2016-11-17 20:59:55]

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

[commit-bot: I haz the power, 2016-11-17 20:59:56]

Try jobs failed on following builders:
  mac_chromium_rel_ng on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

[flackr, 2016-11-18 03:14:05]

The CQ bit was checked by flackr@chromium.org

[flackr, 2016-11-18 03:14:05]

The patchset sent to the CQ was uploaded after l-g-t-m from
weiliangc@chromium.org
Link to the patchset: https://codereview.chromium.org/2511473003/#ps40001
(title: "Update test.")

[commit-bot: I haz the power, 2016-11-18 03:16:03]

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, 2016-11-18 04:17:57]

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

[commit-bot: I haz the power, 2016-11-18 04:17:58]

Try jobs failed on following builders:
  linux_android_rel_ng on master.tryserver.chromium.android (JOB_FAILED,
https://build.chromium.org/p/tryserver.chromium.android/builders/linux_androi...)

[flackr, 2016-11-18 15:53:09]

flackr@chromium.org changed reviewers:
+ boliu@chromium.org

[flackr, 2016-11-18 15:53:09]

+boliu for android_webview test update.

[boliu, 2016-11-18 16:51:19]

lgtm

[flackr, 2016-11-18 16:57:53]

The CQ bit was checked by flackr@chromium.org

[flackr, 2016-11-18 16:57:53]

The patchset sent to the CQ was uploaded after l-g-t-m from
weiliangc@chromium.org
Link to the patchset: https://codereview.chromium.org/2511473003/#ps60001
(title: "Round target scroll position in android test.")

[commit-bot: I haz the power, 2016-11-18 16:58:39]

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, 2016-11-18 19:05:09]

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

[commit-bot: I haz the power, 2016-11-18 19:05:10]

Try jobs failed on following builders:
  linux_trusty_blink_rel on master.tryserver.blink (JOB_FAILED,
http://build.chromium.org/p/tryserver.blink/builders/linux_trusty_blink_rel/b...)

[flackr, 2016-11-21 21:24:31]

The CQ bit was checked by flackr@chromium.org

[flackr, 2016-11-21 21:24:32]

The patchset sent to the CQ was uploaded after l-g-t-m from
weiliangc@chromium.org, boliu@chromium.org
Link to the patchset: https://codereview.chromium.org/2511473003/#ps80001
(title: "Ensure previous test has been completed before starting next test in
scroll-interruption-test.")

[commit-bot: I haz the power, 2016-11-21 21:25:06]

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, 2016-11-21 23:44:59]

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

[commit-bot: I haz the power, 2016-11-21 23:45:00]

Try jobs failed on following builders:
  linux_trusty_blink_rel on master.tryserver.blink (JOB_FAILED,
http://build.chromium.org/p/tryserver.blink/builders/linux_trusty_blink_rel/b...)

[flackr, 2016-11-22 22:06:28]

The CQ bit was checked by flackr@chromium.org

[flackr, 2016-11-22 22:06:29]

The patchset sent to the CQ was uploaded after l-g-t-m from
weiliangc@chromium.org, boliu@chromium.org
Link to the patchset: https://codereview.chromium.org/2511473003/#ps100001
(title: "Wait for scroll animation to complete before checking main thread
scrolling reasons.")

[commit-bot: I haz the power, 2016-11-22 22:07:01]

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, 2016-11-22 23:39:37]

CQ is committing da patch.

Bot data: {"patchset_id": 100001, "attempt_start_ts": 1479852388580020,
"parent_rev": "ea60ced354a9f9855d58563696638f58da229dba", "commit_rev":
"25eb4ae80ab554c1eae9726388e245ef95952611"}

[commit-bot: I haz the power, 2016-11-22 23:40:04]

Committed patchset #6 (id:100001)

[commit-bot: I haz the power, 2016-11-22 23:42:27]

Description was changed from

==========
Round the scroll offset synced back to main instead of flooring.

When scrolling up, flooring the scroll delta sent back to main can result
in main thinking that we have scrolled up by a pixel while cc still positions
layers as if we are at the old scroll position. To be technically correct
according to the frame that will be produced, we would need to round according
to the current scroll snap size but this isn ot easily known at the time of
rounding so we use the nearest integer since this is the common case.

BUG=663291
TEST=LayerTreeHostImplTest.SyncSubpixelScrollDelta
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel
==========

to

==========
Round the scroll offset synced back to main instead of flooring.

When scrolling up, flooring the scroll delta sent back to main can result
in main thinking that we have scrolled up by a pixel while cc still positions
layers as if we are at the old scroll position. To be technically correct
according to the frame that will be produced, we would need to round according
to the current scroll snap size but this isn ot easily known at the time of
rounding so we use the nearest integer since this is the common case.

BUG=663291
TEST=LayerTreeHostImplTest.SyncSubpixelScrollDelta
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel

Committed: https://crrev.com/75a7e4cb1ec29ded2e52539259233356caa883c8
Cr-Commit-Position: refs/heads/master@{#434022}
==========

[commit-bot: I haz the power, 2016-11-22 23:42:28]

Patchset 6 (id:??) landed as
https://crrev.com/75a7e4cb1ec29ded2e52539259233356caa883c8
Cr-Commit-Position: refs/heads/master@{#434022}