Load webview based GAIA in hidden state and pass focus when ready

Load webview based GAIA in hidden state and pass focus when ready

This patch re-enabled GAIA preloading, removes 'focusready' message per agreement and
add focus passing logic.

BUG=462337
TEST=manual

Committed: https://crrev.com/588c2d98ad0f1f4f29d6b93ad37ea5060f297477
Cr-Commit-Position: refs/heads/master@{#319893}

[Dmitry Polukhin, 2015-03-10 12:23:03]

dpolukhin@chromium.org changed reviewers:
+ nkostylev@chromium.org

[Dmitry Polukhin, 2015-03-10 12:23:03]

PTAL

[Nikita (slow), 2015-03-10 12:43:18]

Please also reference 456118

[Nikita (slow), 2015-03-10 12:45:02]

lgtm

[Dmitry Polukhin, 2015-03-10 14:32:11]

The CQ bit was checked by dpolukhin@chromium.org

[commit-bot: I haz the power, 2015-03-10 14:32:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/995753002/1

[commit-bot: I haz the power, 2015-03-10 16:04:27]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-10 16:05:12]

Patchset 1 (id:??) landed as
https://crrev.com/588c2d98ad0f1f4f29d6b93ad37ea5060f297477
Cr-Commit-Position: refs/heads/master@{#319893}