<webview> + <extensionview>: Create a maybeHandleMutation call into attributes

<webview> + <extensionview>: Create a maybeHandleMutation call into attributes

web_view.js and extension_view.js call into maybeHandleMutation which will call
handleMutation if the mutation is not set to be ignored. This removes access to
the ignoreMutation field outside of attribute objects.

This CL also fixes a bug in extensionview src attribute where it does not access
the ignoreMutation field properly.

BUG=none
TBR=lazyboy@chromium.org

Committed: https://crrev.com/75868fc9ef79b39e63c7069d4ba95b24489f31e5
Cr-Commit-Position: refs/heads/master@{#316273}

[Fady Samuel, 2015-02-13 17:10:45]

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

[Fady Samuel, 2015-02-13 17:10:45]

+paulmeyer@ for web_view* changes
+apacible@ for extension_view* changes.

Thanks!

[Fady Samuel, 2015-02-13 17:18:08]

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

[apacible, 2015-02-13 18:21:22]

lgtm

extension_view* lgtm

Thanks!

[paulmeyer, 2015-02-13 18:29:12]

web_view* LGTM!

[Fady Samuel, 2015-02-13 19:17:15]

The CQ bit was checked by fsamuel@chromium.org

[commit-bot: I haz the power, 2015-02-13 19:18:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/929453002/20001

[commit-bot: I haz the power, 2015-02-13 19:18:03]

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

[commit-bot: I haz the power, 2015-02-13 19:18:04]

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.

[Fady Samuel, 2015-02-13 19:19:40]

The CQ bit was checked by fsamuel@chromium.org

[commit-bot: I haz the power, 2015-02-13 19:21:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/929453002/20001

[commit-bot: I haz the power, 2015-02-13 20:27:27]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-02-13 20:27:58]

Patchset 2 (id:??) landed as
https://crrev.com/75868fc9ef79b39e63c7069d4ba95b24489f31e5
Cr-Commit-Position: refs/heads/master@{#316273}