Cleanup after M

Cleanup after M

Remove the reference to preview_sources from GN build file. Once
this lands, next step is removing the actual source file
from android_tools.

BUG=512264
Committed: https://crrev.com/7c8e7090a85c023084b130f1c1a666fa93aeb151
Cr-Commit-Position: refs/heads/master@{#353925}

[sgurun-gerrit only, 2015-10-13 22:23:21]

sgurun@chromium.org changed reviewers:
+ jbudorick@chromium.org

[sgurun-gerrit only, 2015-10-13 22:23:37]

On 2015/10/13 22:23:21, sgurun wrote:
> mailto:sgurun@chromium.org changed reviewers:
> + mailto:jbudorick@chromium.org

ptal, thanks

[jbudorick, 2015-10-13 23:40:40]

lgtm

[sgurun-gerrit only, 2015-10-13 23:44:59]

The CQ bit was checked by sgurun@chromium.org

[commit-bot: I haz the power, 2015-10-13 23:45:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1399543004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1399543004/1

[commit-bot: I haz the power, 2015-10-14 00:37:47]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-14 00:38:29]

Patchset 1 (id:??) landed as
https://crrev.com/7c8e7090a85c023084b130f1c1a666fa93aeb151
Cr-Commit-Position: refs/heads/master@{#353925}