Make CanvasRenderingContext not inherit from ActiveDOMObject

Make CanvasRenderingContext not inherit from ActiveDOMObject

The first step before sharing CanvasRenderingContext (CRC) between
HTMLCanvasElement and OffscreenCanvas is to take away the inheritance
relationship between CRC and ActiveDOMObject. It is not right that both
HTMLCanvasElement and its associated CRC are monitoring Document separately.
Instead, we add willDetachDocument() to DocumentVisibilityObserver, so that
when Document is detached, HTMLCanvasElement will notice this change and call
willDetachDocument() to promptly propagates the change to its associated CRC,
and CRC will invoke stop() to lose context.

BUG=563826
Committed: https://crrev.com/9c74567e241b46365ecb48f88c62ff5b993ae2bb
Cr-Commit-Position: refs/heads/master@{#373711}

[xlai (Olivia), 2016-02-04 20:25:21]

xlai@chromium.org changed reviewers:
+ junov@chromium.org

[Justin Novosad, 2016-02-04 21:31:38]

lgtm with nit

https://codereview.chromium.org/1662423002/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/dom/DocumentVisibilityObserver.h (right):

https://codereview.chromium.org/1662423002/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/dom/DocumentVisibilityObserver.h:23: virtual void
willDetachDocument() { };
You could make this pure virtual ("= 0;" instead of "{ }")

[xlai (Olivia), 2016-02-04 21:57:12]

Patchset #2 (id:10001) has been deleted

[xlai (Olivia), 2016-02-04 22:08:12]

The CQ bit was checked by xlai@chromium.org

[xlai (Olivia), 2016-02-04 22:08:12]

The patchset sent to the CQ was uploaded after l-g-t-m from junov@chromium.org
Link to the patchset: https://codereview.chromium.org/1662423002/#ps30001
(title: "Make the function pure virtual")

[commit-bot: I haz the power, 2016-02-04 22:11:16]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1662423002/30001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1662423002/30001

[commit-bot: I haz the power, 2016-02-05 01:46:37]

Committed patchset #2 (id:30001)

[commit-bot: I haz the power, 2016-02-05 01:47:59]

Description was changed from

==========
Make CanvasRenderingContext not inherit from ActiveDOMObject

The first step before sharing CanvasRenderingContext (CRC) between
HTMLCanvasElement and OffscreenCanvas is to take away the inheritance
relationship between CRC and ActiveDOMObject. It is not right that both
HTMLCanvasElement and its associated CRC are monitoring Document separately.
Instead, we add willDetachDocument() to DocumentVisibilityObserver, so that
when Document is detached, HTMLCanvasElement will notice this change and call
willDetachDocument() to promptly propagates the change to its associated CRC,
and CRC will invoke stop() to lose context.

BUG=563826
==========

to

==========
Make CanvasRenderingContext not inherit from ActiveDOMObject

The first step before sharing CanvasRenderingContext (CRC) between
HTMLCanvasElement and OffscreenCanvas is to take away the inheritance
relationship between CRC and ActiveDOMObject. It is not right that both
HTMLCanvasElement and its associated CRC are monitoring Document separately.
Instead, we add willDetachDocument() to DocumentVisibilityObserver, so that
when Document is detached, HTMLCanvasElement will notice this change and call
willDetachDocument() to promptly propagates the change to its associated CRC,
and CRC will invoke stop() to lose context.

BUG=563826

Committed: https://crrev.com/9c74567e241b46365ecb48f88c62ff5b993ae2bb
Cr-Commit-Position: refs/heads/master@{#373711}
==========

[commit-bot: I haz the power, 2016-02-05 01:48:00]

Patchset 2 (id:??) landed as
https://crrev.com/9c74567e241b46365ecb48f88c62ff5b993ae2bb
Cr-Commit-Position: refs/heads/master@{#373711}