Oilpan: handle WorkerObjectProxy::m_executionContext ref better.

Oilpan: handle WorkerObjectProxy::m_executionContext ref better.

The proxy object outlives its ExecutionContext reference; exempt it
from any GC plugin checks.

R=
BUG=553613
Committed: https://crrev.com/1a57fcd05d963bcfda687e63b958602b1ced20f8
Cr-Commit-Position: refs/heads/master@{#359162}

[sof, 2015-11-11 19:37:30]

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

[sof, 2015-11-11 19:37:30]

please take a look.

[haraken, 2015-11-11 19:39:20]

LGTM

(I'd replace it with UntracedMember (to enable the use-after-free detection) in
the future though.)

[sof, 2015-11-11 19:40:13]

The CQ bit was checked by sigbjornf@opera.com

[commit-bot: I haz the power, 2015-11-11 19:40:49]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1438823002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1438823002/1

[commit-bot: I haz the power, 2015-11-11 19:53:39]

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

[commit-bot: I haz the power, 2015-11-11 19:53:40]

Try jobs failed on following builders:
  win_chromium_compile_dbg_ng on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_comp...)

[sof, 2015-11-11 20:20:51]

The CQ bit was checked by sigbjornf@opera.com

[commit-bot: I haz the power, 2015-11-11 20:22:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1438823002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1438823002/1

[commit-bot: I haz the power, 2015-11-11 21:37:54]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-12 20:00:41]

Patchset 1 (id:??) landed as
https://crrev.com/1a57fcd05d963bcfda687e63b958602b1ced20f8
Cr-Commit-Position: refs/heads/master@{#359162}