Merged r15782 into 3.19 branch.

Merged r15782 into 3.19 branch.

Fix unaligned accesses in back_edge tables.

R=jkummerow@chromium.org
BUG=

[palfia, 2013-07-22 19:18:08]

PTAL.

[Jakob Kummerow, 2013-07-23 08:01:56]

We usually don't back-merge performance improvements, only
crash/correctness/security fixes. You'll have to give me a pretty good reason
why this warrants an exception.

[Paul Lind, 2013-07-23 18:28:41]

This is fixing a small performance regression, which is subtly different than
performance improvement. However, the key point is that it is "small". I cannot
make a strong case why we need this if it conflicts with normal policy. We can
drop this one, and related https://codereview.chromium.org/19846005/.

FYI, without the patch we take about 2100 alignment exception fixups in the
kernel while running Octane, but the net result is just about un-measurable in
terms of final score, which is how we missed it for so long. We have fixed our
bots to flag errors on these cases, so we won't miss even the rare ones going
forward.

[Jakob Kummerow, 2013-07-23 19:14:05]

I don't feel strongly about it either way, but "just about un-measurable"
doesn't sound like this needs to be merged back. The beauty of our 6-week
release cycle is that we can have a very conservative policy for backmerges, and
fixes get out to users rather quickly anyway. So I would prefer to just close
this.

[Paul Lind, 2013-07-23 19:21:38]

Agreed, thanks for explaining the policy, which I had not fully understood.
Ákos, can you please close these two issues?

[palfia, 2013-07-23 19:24:21]

Closing issue..