Add proguard pre-processing of google_play_services.

Add proguard pre-processing of google_play_services.

The GN build was missing the proguarding directives. Update to match gyp.
BUG=502891
Committed: https://crrev.com/daa7193c7f0573fe4135404e134db060348dde8c
Cr-Commit-Position: refs/heads/master@{#335594}

[Yaron, 2015-06-22 19:00:03]

yfriedman@chromium.org changed reviewers:
+ cjhopman@chromium.org

[Dirk Pranke, 2015-06-22 20:47:10]

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

[Dirk Pranke, 2015-06-22 20:47:10]

lgtm, though you probably still need cjhopman's approval as well.

[Yaron, 2015-06-23 00:28:33]

On 2015/06/22 20:47:10, Dirk Pranke wrote:
> lgtm, though you probably still need cjhopman's approval as well.

the reitveld extension looks green and this is pretty harmless so here goes
nothing

[Yaron, 2015-06-23 00:28:40]

The CQ bit was checked by yfriedman@chromium.org

[commit-bot: I haz the power, 2015-06-23 00:29:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1200953002/1

[commit-bot: I haz the power, 2015-06-23 00:34:58]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-23 00:35:40]

Patchset 1 (id:??) landed as
https://crrev.com/daa7193c7f0573fe4135404e134db060348dde8c
Cr-Commit-Position: refs/heads/master@{#335594}