PPC: Simplify pending message script handling.

PPC: Simplify pending message script handling.

Port f71e26268338d2840133264329bf35a63011bb5a

Original commit message:
This removes the separate tracking of the pending message script,
because that script is already stored in the message object and
duplicating it in the ThreadLocalTop makes it more brittle.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/995013005

Cr-Commit-Position: refs/heads/master@{#27127}

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

BUG=

Committed: https://crrev.com/c67dab62c7db38a31de853418874d99b7ae97a3b
Cr-Commit-Position: refs/heads/master@{#27144}

[michael_dawson, 2015-03-11 17:08:42]

PPC Change to resolve latest breaking change in common files

[Benedikt Meurer, 2015-03-12 04:04:03]

lgtm

[Benedikt Meurer, 2015-03-12 04:04:07]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2015-03-12 04:04:16]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/999093002/1

[commit-bot: I haz the power, 2015-03-12 04:27:16]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-12 04:27:31]

Patchset 1 (id:??) landed as
https://crrev.com/c67dab62c7db38a31de853418874d99b7ae97a3b
Cr-Commit-Position: refs/heads/master@{#27144}