Clean up some GN toolchain args, especially NaCl.

Clean up some GN toolchain args, especially NaCl.

Uses forward_variables_from for the gcc_toolchain and nacl_toolchain templates
when applicable.

Add the ability to clear the sanitizer flags and use this for nacl.

Committed: https://crrev.com/f5d97233985fac498ada3def2c2b3f4e8bbaafd9
Cr-Commit-Position: refs/heads/master@{#348522}

[brettw, 2015-09-11 20:39:37]

brettw@chromium.org changed reviewers:
+ dpranke@chromium.org

[brettw, 2015-09-11 20:39:41]

The CQ bit was checked by brettw@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-09-11 20:40:36]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1338803004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1338803004/1

[Dirk Pranke, 2015-09-11 20:42:31]

lgtm

[brettw, 2015-09-11 20:42:46]

The CQ bit was unchecked by brettw@chromium.org

[brettw, 2015-09-11 20:42:47]

The CQ bit was checked by brettw@chromium.org

[commit-bot: I haz the power, 2015-09-11 20:44:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1338803004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1338803004/1

[commit-bot: I haz the power, 2015-09-12 00:05:39]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-12 00:05:40]

Try jobs failed on following builders:
  linux_chromium_gn_chromeos_rel on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[brettw, 2015-09-12 02:02:34]

The CQ bit was checked by brettw@chromium.org

[commit-bot: I haz the power, 2015-09-12 02:04:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1338803004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1338803004/1

[commit-bot: I haz the power, 2015-09-12 03:04:29]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-12 03:05:06]

Patchset 1 (id:??) landed as
https://crrev.com/f5d97233985fac498ada3def2c2b3f4e8bbaafd9
Cr-Commit-Position: refs/heads/master@{#348522}

[commit-bot: I haz the power, 2015-09-23 12:27:46]

Patchset 1 (id:??) landed as
https://crrev.com/f5d97233985fac498ada3def2c2b3f4e8bbaafd9
Cr-Commit-Position: refs/heads/master@{#348522}