Split the GN 'snapshot_toolchain' logic out into an include file.

Split the GN 'snapshot_toolchain' logic out into an include file.

We need to build parts of v8 with a toolchain that might be different
from both the default (target) toolchain and the regular host toolchain,
because we need the snapshot to have the same bit-width as the target.
V8's build defines a 'snapshot_toolchain' setting for this.

It turns out that we need the value of this toolchain to be exposed
to the Chromium build because some of the test targets (in browser_tests)
depend on d8 and need to be able to built using the same toolchain.

R=brett@chromium.org, jochen@chromium.org
BUG=

Committed: https://crrev.com/7d5d1570d9eb716f6f869274c0df277bc71328dd
Cr-Commit-Position: refs/heads/master@{#30854}

[Dirk Pranke, 2015-09-19 00:50:57]

Please take a look and let me know if I'm missing something or if there's a
better way to accomplish this.

For context, here's the Chromium CL that needs this:

https://codereview.chromium.org/1359513002/

[jochen (gone - plz use gerrit), 2015-09-21 15:10:49]

lgtm with comment

https://codereview.chromium.org/1350223004/diff/1/snapshot_toolchain.gni
File snapshot_toolchain.gni (right):

https://codereview.chromium.org/1350223004/diff/1/snapshot_toolchain.gni#newc...
snapshot_toolchain.gni:1: # Copyright 2014 The Chromium Authors. All rights
reserved.
please use the v8 license header. Essentially "The V8 project authors" instead
of "THe Chromium Authors"

[Dirk Pranke, 2015-09-21 20:48:57]

On 2015/09/21 15:10:49, jochen wrote:
> lgtm with comment
> 
> https://codereview.chromium.org/1350223004/diff/1/snapshot_toolchain.gni
> File snapshot_toolchain.gni (right):
> 
>
https://codereview.chromium.org/1350223004/diff/1/snapshot_toolchain.gni#newc...
> snapshot_toolchain.gni:1: # Copyright 2014 The Chromium Authors. All rights
> reserved.
> please use the v8 license header. Essentially "The V8 project authors" instead
> of "THe Chromium Authors"

Ah, right, of course.

[Dirk Pranke, 2015-09-22 01:14:08]

Header fixed.

[Dirk Pranke, 2015-09-22 01:14:11]

The CQ bit was checked by dpranke@chromium.org

[Dirk Pranke, 2015-09-22 01:14:12]

The patchset sent to the CQ was uploaded after l-g-t-m from jochen@chromium.org
Link to the patchset: https://codereview.chromium.org/1350223004/#ps20001
(title: "update license header")

[commit-bot: I haz the power, 2015-09-22 01:14:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1350223004/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1350223004/20001

[commit-bot: I haz the power, 2015-09-22 02:28:38]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-09-22 02:28:51]

Patchset 2 (id:??) landed as
https://crrev.com/7d5d1570d9eb716f6f869274c0df277bc71328dd
Cr-Commit-Position: refs/heads/master@{#30854}