Add a GN import for sanitizers.gni.

Add a GN import for sanitizers.gni.

The is_*san flags are moving from the master build config file into this
.gni file. This patch will allow V8 to continue compiling when that change
is landed.

Committed: https://crrev.com/0014ad92a3fa308402140016a2b50be6d169779e
Cr-Commit-Position: refs/heads/master@{#30623}

[brettw, 2015-09-04 21:33:32]

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

[jochen (gone - plz use gerrit), 2015-09-07 14:24:53]

The CQ bit was checked by jochen@chromium.org

[jochen (gone - plz use gerrit), 2015-09-07 14:24:53]

lgtm

[commit-bot: I haz the power, 2015-09-07 14:24:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1330713003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1330713003/1

[commit-bot: I haz the power, 2015-09-07 15:22:49]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-07 15:23:08]

Patchset 1 (id:??) landed as
https://crrev.com/0014ad92a3fa308402140016a2b50be6d169779e
Cr-Commit-Position: refs/heads/master@{#30623}