Free context resources when memory limit is 0

Free context resources when memory limit is 0

Android webview does not use chrome's concept of visibility. Treat
memory being set to 0 as signal to drop memory. And drop memory by
flipping the surface to invisible and back.

BUG=496057
Committed: https://crrev.com/b032a08db9fbaedacaa5b0ac4d39374c4995839c
Cr-Commit-Position: refs/heads/master@{#333113}

[boliu, 2015-06-05 16:14:34]

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

[boliu, 2015-06-05 16:14:35]

I think this kinda works..

saves about 16 out of the 20M regression when webview started keeping context
alive, but then don't send visibility signals to it like chrome does

[boliu, 2015-06-05 16:37:10]

The CQ bit was checked by boliu@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-06-05 16:38:15]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1164083003/40001

[commit-bot: I haz the power, 2015-06-05 17:06:48]

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

[commit-bot: I haz the power, 2015-06-05 17:06:51]

Dry run: This issue passed the CQ dry run.

[no sievers, 2015-06-05 18:21:48]

lgtm

[boliu, 2015-06-05 18:22:38]

The CQ bit was checked by boliu@chromium.org

[commit-bot: I haz the power, 2015-06-05 18:24:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1164083003/60001

[commit-bot: I haz the power, 2015-06-05 20:03:24]

Committed patchset #4 (id:60001)

[commit-bot: I haz the power, 2015-06-05 20:04:19]

Patchset 4 (id:??) landed as
https://crrev.com/b032a08db9fbaedacaa5b0ac4d39374c4995839c
Cr-Commit-Position: refs/heads/master@{#333113}