Allow opting out of thumb mode for ARM builds.

Allow opting out of thumb mode for ARM builds.

Heap profiler relies on frame pointers to do stack unwinding. ARM builds
are using thumb mode by default, but since frame pointers are broken in thumb
mode for both GCC and LLVM (https://llvm.org/bugs/show_bug.cgi?id=18505), we
need a way to build in arm mode.

This change exposes arm_use_thumb GN variable so that it can be set to false.

BUG=602701
Committed: https://crrev.com/2a91d261e9858e3914153f0fc3d0f57a4b126558
Cr-Commit-Position: refs/heads/master@{#393615}

[Dmitry Skiba, 2016-05-12 17:59:48]

dskiba@google.com changed reviewers:
+ dpranke@chromium.org

[Dirk Pranke, 2016-05-12 18:12:04]

lgtm

[Dmitry Skiba, 2016-05-13 17:55:15]

The CQ bit was checked by dskiba@google.com

[commit-bot: I haz the power, 2016-05-13 17:55:42]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1977533002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1977533002/1

[commit-bot: I haz the power, 2016-05-13 20:34:09]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-05-13 20:35:17]

Description was changed from

==========
Allow opting out of thumb mode for ARM builds.

Heap profiler relies on frame pointers to do stack unwinding. ARM builds
are using thumb mode by default, but since frame pointers are broken in thumb
mode for both GCC and LLVM (https://llvm.org/bugs/show_bug.cgi?id=18505), we
need a way to build in arm mode.

This change exposes arm_use_thumb GN variable so that it can be set to false.

BUG=602701
==========

to

==========
Allow opting out of thumb mode for ARM builds.

Heap profiler relies on frame pointers to do stack unwinding. ARM builds
are using thumb mode by default, but since frame pointers are broken in thumb
mode for both GCC and LLVM (https://llvm.org/bugs/show_bug.cgi?id=18505), we
need a way to build in arm mode.

This change exposes arm_use_thumb GN variable so that it can be set to false.

BUG=602701

Committed: https://crrev.com/2a91d261e9858e3914153f0fc3d0f57a4b126558
Cr-Commit-Position: refs/heads/master@{#393615}
==========

[commit-bot: I haz the power, 2016-05-13 20:35:18]

Patchset 1 (id:??) landed as
https://crrev.com/2a91d261e9858e3914153f0fc3d0f57a4b126558
Cr-Commit-Position: refs/heads/master@{#393615}