Android: Handle readback helper context init failure

Android: Handle readback helper context init failure

We should not attempt to create a GLHelper with a null
GLES2Impl (it will crash), which is the case if context
init failed.

BUG=439363
NOTRY=True

Committed: https://crrev.com/26e88baf416c3ed31c1f465d3ac42315bae22050
Cr-Commit-Position: refs/heads/master@{#307080}

[no sievers, 2014-12-05 19:49:29]

sievers@chromium.org changed reviewers:
+ danakj@chromium.org

[no sievers, 2014-12-05 19:50:31]

ptal

[danakj, 2014-12-05 20:59:55]

LGTM

[no sievers, 2014-12-05 21:00:40]

The CQ bit was checked by sievers@chromium.org

[commit-bot: I haz the power, 2014-12-05 21:01:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/786473002/1

[no sievers, 2014-12-05 21:11:03]

The CQ bit was unchecked by sievers@chromium.org

[no sievers, 2014-12-05 21:11:12]

The CQ bit was checked by sievers@chromium.org

[commit-bot: I haz the power, 2014-12-05 21:11:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/786473002/1

[commit-bot: I haz the power, 2014-12-05 21:12:15]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-12-05 21:13:46]

Patchset 1 (id:??) landed as
https://crrev.com/26e88baf416c3ed31c1f465d3ac42315bae22050
Cr-Commit-Position: refs/heads/master@{#307080}