Speculative fix for ui::DisplayLinkMac::StopDisplayLink crashes #take2.

Speculative fix for ui::DisplayLinkMac::StopDisplayLink crashes #take2.

The CVDisplayLink is tied to a ScopedTypeRef data member of DisplayLinkMac.
However, there may be other references. Since there's no guarantee that
~DisplayLinkMac() will invoke the last CVDisplayLinkRelease(..) and clear
the callback automatically, clear it explicitly in ~DisplayLinkMac.

BUG=564780
Committed: https://crrev.com/119ecfdddd45db9e5e74d0d6a6eb4d9423cec8f2
Cr-Commit-Position: refs/heads/master@{#372046}

[tapted, 2016-01-28 07:06:08]

Patchset #2 (id:20001) has been deleted

[tapted, 2016-01-28 07:10:51]

Description was changed from

==========
Speculative fix for ui::DisplayLinkMac::StopDisplayLink crashes

The CVDisplayLink is tied to a ScopedTypeRef data member of DisplayLinkMac.
However, there may be other references. Since there's no guarantee that
~DisplayLinkMac() will invoke the last CVDisplayLinkRelease(..) and clear
the callback automatically, clear it explicitly in ~DisplayLinkMac.

BUG=564780
==========

to

==========
Speculative fix for ui::DisplayLinkMac::StopDisplayLink crashes #take2.

The CVDisplayLink is tied to a ScopedTypeRef data member of DisplayLinkMac.
However, there may be other references. Since there's no guarantee that
~DisplayLinkMac() will invoke the last CVDisplayLinkRelease(..) and clear
the callback automatically, clear it explicitly in ~DisplayLinkMac.

BUG=564780
==========

[tapted, 2016-01-28 07:11:20]

tapted@chromium.org changed reviewers:
+ ccameron@chromium.org

[tapted, 2016-01-28 07:11:21]

Hi Chris - please take a look. (my dev machine was wedged in a state where it
couldn't get xcode 7 - turns out the SDK there doesn't let you have a null
callback at compile time (even though it seems to work fine at runtime grumble).

So, this isn't as pretty. We could use the same callback, change |context| to
null and check for it, but this approach seems cleaner, if a little verbose.

[ccameron, 2016-01-28 07:23:10]

lgtm

[tapted, 2016-01-28 07:25:12]

The CQ bit was checked by tapted@chromium.org

[commit-bot: I haz the power, 2016-01-28 07:25:24]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1637353002/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1637353002/40001

[commit-bot: I haz the power, 2016-01-28 08:01:09]

Description was changed from

==========
Speculative fix for ui::DisplayLinkMac::StopDisplayLink crashes #take2.

The CVDisplayLink is tied to a ScopedTypeRef data member of DisplayLinkMac.
However, there may be other references. Since there's no guarantee that
~DisplayLinkMac() will invoke the last CVDisplayLinkRelease(..) and clear
the callback automatically, clear it explicitly in ~DisplayLinkMac.

BUG=564780
==========

to

==========
Speculative fix for ui::DisplayLinkMac::StopDisplayLink crashes #take2.

The CVDisplayLink is tied to a ScopedTypeRef data member of DisplayLinkMac.
However, there may be other references. Since there's no guarantee that
~DisplayLinkMac() will invoke the last CVDisplayLinkRelease(..) and clear
the callback automatically, clear it explicitly in ~DisplayLinkMac.

BUG=564780
==========

[commit-bot: I haz the power, 2016-01-28 08:01:10]

Committed patchset #2 (id:40001)

[commit-bot: I haz the power, 2016-01-28 08:02:56]

Description was changed from

==========
Speculative fix for ui::DisplayLinkMac::StopDisplayLink crashes #take2.

The CVDisplayLink is tied to a ScopedTypeRef data member of DisplayLinkMac.
However, there may be other references. Since there's no guarantee that
~DisplayLinkMac() will invoke the last CVDisplayLinkRelease(..) and clear
the callback automatically, clear it explicitly in ~DisplayLinkMac.

BUG=564780
==========

to

==========
Speculative fix for ui::DisplayLinkMac::StopDisplayLink crashes #take2.

The CVDisplayLink is tied to a ScopedTypeRef data member of DisplayLinkMac.
However, there may be other references. Since there's no guarantee that
~DisplayLinkMac() will invoke the last CVDisplayLinkRelease(..) and clear
the callback automatically, clear it explicitly in ~DisplayLinkMac.

BUG=564780

Committed: https://crrev.com/119ecfdddd45db9e5e74d0d6a6eb4d9423cec8f2
Cr-Commit-Position: refs/heads/master@{#372046}
==========

[commit-bot: I haz the power, 2016-01-28 08:02:57]

Patchset 2 (id:??) landed as
https://crrev.com/119ecfdddd45db9e5e74d0d6a6eb4d9423cec8f2
Cr-Commit-Position: refs/heads/master@{#372046}