Update element_id class comment to reflect how element id works

Update element_id class comment to reflect how element id works

This patch updates the element_id comment to describe the modern use
of element ids in the compositor and blink.

BUG=693740
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel

Review-Url: https://codereview.chromium.org/2826703003
Cr-Commit-Position: refs/heads/master@{#465400}
Committed: https://chromium.googlesource.com/chromium/src/+/315f18b6f11170412ef3e9057cb84eeaf24322b6

[pdr., 2017-04-18 18:18:22]

Description was changed from

==========
Update element_id class comment to reflect how element id works

This patch updates the element_id comment to describe the modern use
of element ids in the compositor and blink.

BUG=693740
==========

to

==========
Update element_id class comment to reflect how element id works

This patch updates the element_id comment to describe the modern use
of element ids in the compositor and blink.

BUG=693740
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel
==========

[pdr., 2017-04-18 18:18:57]

pdr@chromium.org changed reviewers:
+ ajuma@chromium.org, enne@chromium.org, weiliangc@chromium.org,
wkorman@chromium.org

[pdr., 2017-04-18 18:20:37]

I'm splitting this comment update out of
https://codereview.chromium.org/2816063003 to make the discussion a little
easier. Please nitpick and bikeshed!

[ajuma, 2017-04-18 18:53:57]

https://codereview.chromium.org/2826703003/diff/1/cc/trees/element_id.h
File cc/trees/element_id.h (right):

https://codereview.chromium.org/2826703003/diff/1/cc/trees/element_id.h#newco...
cc/trees/element_id.h:43: // stable identifier for animation targets.
It's worth also mentioning that we currently set ElementIds on layers, and those
can change over the course of the layer's lifetime since, for animations,
non-default ElementIds are only set during the animation's lifetime.

[wkorman, 2017-04-18 20:10:00]

I also found some of the slides in loyso@ presentation very helpful, and the
history useful:

doc:
https://docs.google.com/document/d/11cVwkPIYuelD_k_SNEeRmLYKuvNkqjCG84fzJHZpz...

presentation:
https://docs.google.com/presentation/d/1wfDqSOgt3S5xIhKl-X-BbG0uhTmiQT0SVwzkn...

We could consider linking to this either from comment or in a README.md. I will
be looking at/updating/creating an animation focused README.md soon as part of
the second bullet here: http://crbug.com/691524#c10

[wkorman, 2017-04-18 20:10:38]

lgtm

also I agree w/ ajuma re: enhancing to note layer could gain/lose differing
non-default element ids over its lifetime.

[pdr., 2017-04-18 21:11:41]

Thanks all. I've updated this comment again to include that element ids can
change during animations (I didn't know that!) I also reworded the scrolling
element id section a little after discussion with Enne.

PTAL

[ajuma, 2017-04-18 21:19:35]

Thanks, lgtm

[pdr., 2017-04-18 21:20:52]

The CQ bit was checked by pdr@chromium.org

[pdr., 2017-04-18 21:20:53]

The patchset sent to the CQ was uploaded after l-g-t-m from wkorman@chromium.org
Link to the patchset: https://codereview.chromium.org/2826703003/#ps20001
(title: "Address reviewer comments and incorporate discussion with Enne")

[commit-bot: I haz the power, 2017-04-18 21:21:37]

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, 2017-04-18 22:30:57]

CQ is committing da patch.

Bot data: {"patchset_id": 20001, "attempt_start_ts": 1492550452803170,
"parent_rev": "a9ee1ac2ffca6fe5d05f0283820ddb1673c2f197", "commit_rev":
"315f18b6f11170412ef3e9057cb84eeaf24322b6"}

[commit-bot: I haz the power, 2017-04-18 22:35:00]

Description was changed from

==========
Update element_id class comment to reflect how element id works

This patch updates the element_id comment to describe the modern use
of element ids in the compositor and blink.

BUG=693740
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel
==========

to

==========
Update element_id class comment to reflect how element id works

This patch updates the element_id comment to describe the modern use
of element ids in the compositor and blink.

BUG=693740
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel

Review-Url: https://codereview.chromium.org/2826703003
Cr-Commit-Position: refs/heads/master@{#465400}
Committed:
https://chromium.googlesource.com/chromium/src/+/315f18b6f11170412ef3e9057cb8...
==========

[commit-bot: I haz the power, 2017-04-18 22:35:00]

Committed patchset #2 (id:20001) as
https://chromium.googlesource.com/chromium/src/+/315f18b6f11170412ef3e9057cb8...