Add unit test for non-leftmost GC mixin instance.

Add unit test for non-leftmost GC mixin instance.

Verify that deriving from a USING_GARBAGE_COLLECTED_MIXIN() annotated
class is traced as expected.

R=haraken
BUG=

Committed: https://crrev.com/baf05aeed31681a87d8eaf85df7f4813b9ab4aaa
Cr-Commit-Position: refs/heads/master@{#361072}

[sof, 2015-11-22 22:01:43]

sigbjornf@opera.com changed reviewers:
+ oilpan-reviews@chromium.org

[sof, 2015-11-22 22:01:44]

please take a look.

[haraken, 2015-11-23 02:41:03]

LGTM

[sof, 2015-11-23 06:18:50]

Description was changed from

==========
Add unit test for non-leftmost GC mixin instance.

Verify that deriving from a USING_GARBAGE_COLLECTED_MIXIN() annotated
class is traced as expected.

R=
BUG=
==========

to

==========
Add unit test for non-leftmost GC mixin instance.

Verify that deriving from a USING_GARBAGE_COLLECTED_MIXIN() annotated
class is traced as expected.

R=haraken
BUG=
==========

[sof, 2015-11-23 06:18:57]

The CQ bit was checked by sigbjornf@opera.com

[sof, 2015-11-23 06:18:57]

The patchset sent to the CQ was uploaded after l-g-t-m from haraken@chromium.org
Link to the patchset: https://codereview.chromium.org/1465083002/#ps20001
(title: "remove temporary, but broken isHeapObjectAlive() testing")

[commit-bot: I haz the power, 2015-11-23 06:19:25]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1465083002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1465083002/20001

[commit-bot: I haz the power, 2015-11-23 06:59:46]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-11-23 07:00:35]

Patchset 2 (id:??) landed as
https://crrev.com/baf05aeed31681a87d8eaf85df7f4813b9ab4aaa
Cr-Commit-Position: refs/heads/master@{#361072}

[sof, 2015-11-23 07:14:20]

Somewhat related, but the GC plugin check we added to insist that a
USING_GARBAGE_COLLECTED_MIXIN()-annotated class also defines a trace(), doesn't
serve a real purpose wrt correctness.