aw: Update pinned prebuilts/ndk revision for libc++ atomic support

aw: Update pinned prebuilts/ndk revision for libc++ atomic support

Update the AOSP prebuilts/ndk target to include fixes necessary to use
libc++ <atomic> on Android.

BUG=427718
Committed: https://crrev.com/4930d365d9c3d4889a3cd061b0440a56f5dae98f
Cr-Commit-Position: refs/heads/master@{#311479}

[jdduke (slow), 2015-01-13 22:34:55]

jdduke@chromium.org changed reviewers:
+ torne@chromium.org

[jdduke (slow), 2015-01-13 22:34:55]

torne@: PTAL, thanks.

[Torne, 2015-01-14 10:24:51]

lgtm

[jdduke (slow), 2015-01-14 10:28:52]

The CQ bit was checked by jdduke@chromium.org

[commit-bot: I haz the power, 2015-01-14 10:29:12]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/846633003/1

[commit-bot: I haz the power, 2015-01-14 10:35:06]

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

[commit-bot: I haz the power, 2015-01-14 10:35:07]

Try jobs failed on following builders:
  ios_dbg_simulator on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_dbg_simulator...)

[jdduke (slow), 2015-01-14 10:36:13]

The CQ bit was checked by jdduke@chromium.org

[commit-bot: I haz the power, 2015-01-14 10:37:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/846633003/1

[commit-bot: I haz the power, 2015-01-14 10:41:42]

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

[commit-bot: I haz the power, 2015-01-14 10:41:44]

Try jobs failed on following builders:
  ios_dbg_simulator on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_dbg_simulator...)

[jdduke (slow), 2015-01-14 15:32:56]

The CQ bit was checked by jdduke@chromium.org

[commit-bot: I haz the power, 2015-01-14 15:33:25]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/846633003/1

[commit-bot: I haz the power, 2015-01-14 15:42:17]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-14 15:43:13]

Patchset 1 (id:??) landed as
https://crrev.com/4930d365d9c3d4889a3cd061b0440a56f5dae98f
Cr-Commit-Position: refs/heads/master@{#311479}