PPC: Simplify pending message object handling.

PPC: Simplify pending message object handling.

Port d4696c484142c601cbd691ae80164043785a3af7

Original commit message:
This moves the decision whether to report a message or not to when
the pending exception is propagated instead of trying to preserve the
decision in a ThreadLocalTop field.

R=titzer@chromium.org

Review URL: https://codereview.chromium.org/998943003

Cr-Commit-Position: refs/heads/master@{#27150}

R=danno@chromium.org, svenpanne@chromium.org, titzer@chromium.org

BUG=

Committed: https://crrev.com/ae78a9702a9e33007e93f79dadfade5c2f22ff14
Cr-Commit-Position: refs/heads/master@{#27173}

[michael_dawson, 2015-03-12 15:30:14]

PPC port for d4696c484142c601cbd691ae80164043785a3af7 Simplify pending message
object handling.

[titzer, 2015-03-12 15:38:50]

lgtm

[Sven Panne, 2015-03-13 07:11:00]

The CQ bit was checked by svenpanne@chromium.org

[commit-bot: I haz the power, 2015-03-13 07:11:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1000963002/1

[commit-bot: I haz the power, 2015-03-13 07:34:52]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-13 07:35:07]

Patchset 1 (id:??) landed as
https://crrev.com/ae78a9702a9e33007e93f79dadfade5c2f22ff14
Cr-Commit-Position: refs/heads/master@{#27173}