Fix WindowAndroid leak in Android WebView

Fix WindowAndroid leak in Android WebView

WebView creates a WindowAndroid class per AwContents, but never calls
destroy on it, so the native WindowAndroid leaks. Do this in
CleanupReference of AwContents.

Also make native WindowAndroid hold a strong reference, so removes
the requirement to null check the ref, which are mostly missing anyway.

Notes:
* This adds the requirement that WindowAndroid cannot hold strong ref
  that would prevent AwContents/ContentViewCore from being gc-ed,
  which currently is the case.
* This does not address the issue that WindowAndroid should be
  per-activity, not per ContentViewCore.

BUG=469803
Committed: https://crrev.com/f1c913e8c18946c07d1a64f118b2d36e1bbe170f
Cr-Commit-Position: refs/heads/master@{#322159}

[boliu, 2015-03-24 21:48:06]

boliu@chromium.org changed reviewers:
+ sievers@chromium.org, tedchoc@chromium.org, torne@chromium.org

[boliu, 2015-03-24 21:48:07]

ptal

feel free to add anyone else that should be notified..

[Ted C, 2015-03-24 22:17:31]

lgtm, this change is fine for chrome for android.

[no sievers, 2015-03-24 23:05:39]

lgtm

[Torne, 2015-03-25 10:12:20]

lgtm

[boliu, 2015-03-25 14:25:04]

The CQ bit was checked by boliu@chromium.org

[commit-bot: I haz the power, 2015-03-25 14:25:30]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1034593002/1

[commit-bot: I haz the power, 2015-03-25 14:49:17]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-25 14:49:56]

Patchset 1 (id:??) landed as
https://crrev.com/f1c913e8c18946c07d1a64f118b2d36e1bbe170f
Cr-Commit-Position: refs/heads/master@{#322159}