Decouple web_view.js from attribute internals

Decouple web_view.js from attribute internals

Hide implementation details of <webview> attribute state from web_view.js.

We introduce a reset method on methods to be called in onElementDetached that
resets the internal state without exposing the details of what that internal
state is.

BUG=none
TBR=lazyboy@chromium.org

Committed: https://crrev.com/09efc6216740c28452cc244cff18d8c33c091239
Cr-Commit-Position: refs/heads/master@{#316294}

[Fady Samuel, 2015-02-13 17:46:01]

fsamuel@chromium.org changed reviewers:
+ paulmeyer@chromium.org

[paulmeyer, 2015-02-13 18:27:18]

LGTM! This is definitely a better way to handle those flags.

[Fady Samuel, 2015-02-13 20:33:14]

New patchsets have been uploaded after l-g-t-m from paulmeyer@chromium.org

[Fady Samuel, 2015-02-13 20:33:35]

The CQ bit was checked by fsamuel@chromium.org

[commit-bot: I haz the power, 2015-02-13 20:35:01]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/926083002/20001

[commit-bot: I haz the power, 2015-02-13 21:34:05]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-02-13 21:35:01]

Patchset 2 (id:??) landed as
https://crrev.com/09efc6216740c28452cc244cff18d8c33c091239
Cr-Commit-Position: refs/heads/master@{#316294}