PPC: Fix trampoline pool blocking.

PPC: Fix trampoline pool blocking.

Check whether a trampoline pool should be emitted after unblocking.
Otherwise, back-to-back sequences which block the trampoline pool can
cause it to be out of reach.

R=joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, dstence@us.ibm.com
BUG=

Committed: https://crrev.com/8779afc9c2f5bb8a2706b323088fc98a648b1337
Cr-Commit-Position: refs/heads/master@{#31945}

[MTBrandyberry, 2015-11-11 16:09:37]

This is the cause of the current buildbot failure.

[JoranSiu, 2015-11-11 16:10:59]

On 2015/11/11 16:09:37, mtbrandyberry wrote:
> This is the cause of the current buildbot failure.

lgtm

[MTBrandyberry, 2015-11-11 16:14:46]

The CQ bit was checked by mbrandy@us.ibm.com

[commit-bot: I haz the power, 2015-11-11 16:14:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1433343002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1433343002/1

[commit-bot: I haz the power, 2015-11-11 16:31:48]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-14 23:20:08]

Patchset 1 (id:??) landed as
https://crrev.com/8779afc9c2f5bb8a2706b323088fc98a648b1337
Cr-Commit-Position: refs/heads/master@{#31945}