Throw if webview has been destroyed

Throw if webview has been destroyed

New APIs can be more strict about enforcing not being called after
destroy.

BUG=457184
Committed: https://crrev.com/b2b11fdea2692c93392b48cbfacce749efc99cf2
Cr-Commit-Position: refs/heads/master@{#319093}

[boliu, 2015-03-04 01:03:38]

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

[boliu, 2015-03-04 01:03:39]

ptal

[Tobias Sargeant, 2015-03-04 16:21:06]

lgtm

[boliu, 2015-03-04 17:20:27]

The CQ bit was checked by boliu@chromium.org

[commit-bot: I haz the power, 2015-03-04 17:20:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/974143002/1

[commit-bot: I haz the power, 2015-03-04 17:20:55]

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

[commit-bot: I haz the power, 2015-03-04 17:20:55]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer,
_not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[boliu, 2015-03-04 17:22:02]

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

[boliu, 2015-03-04 17:22:03]

+hush for committer stamp

[hush (inactive), 2015-03-04 18:40:15]

The CQ bit was checked by hush@chromium.org

[hush (inactive), 2015-03-04 18:40:15]

lgtm

[commit-bot: I haz the power, 2015-03-04 18:41:12]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/974143002/1

[commit-bot: I haz the power, 2015-03-04 19:03:36]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-04 19:04:32]

Patchset 1 (id:??) landed as
https://crrev.com/b2b11fdea2692c93392b48cbfacce749efc99cf2
Cr-Commit-Position: refs/heads/master@{#319093}