<webview>: Fix SrcAttribute and Cleanup

<webview>: Fix SrcAttribute and Cleanup

SrcAttribute.setValueIgnoreMutation was calling takeRecords() prior to applying the operation,
which meant it didn't actually do the right thing. Mutation callbacks would still get queued
up by the mutation observer. This wasn't noticed because WebViewImpl.onLoadCommit only called
setValueIgnoreMutation if there was a change in value, and so the mutation observer would not
trigger any mutations. This CL fixes this issue and simplifies the code in WebViewImpl.onLoadCommit
a bit.

This CL moves setting NameAttribute details from WebViewImpl and into the NameAttribute object.

This CL also fixes some attribute changes to make sure their mutation handlers don't fire.

Finally, this CL moves setupEventProperty to web_view_events.js where it makes more sense to be.

BUG=none
TBR=lazyboy@chromium.org

Committed: https://crrev.com/cab37f85ed91c494e86fc201bf1550b9ba467471
Cr-Commit-Position: refs/heads/master@{#317682}

[Fady Samuel, 2015-02-23 21:34:51]

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

[paulmeyer, 2015-02-23 21:50:38]

LGTM!

[Fady Samuel, 2015-02-23 21:52:39]

The CQ bit was checked by fsamuel@chromium.org

[commit-bot: I haz the power, 2015-02-23 21:53:44]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/954543002/1

[commit-bot: I haz the power, 2015-02-23 23:07:38]

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

[commit-bot: I haz the power, 2015-02-23 23:07:40]

Failed to apply the patch.

[commit-bot: I haz the power, 2015-02-23 23:08:08]

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

[Fady Samuel, 2015-02-23 23:42:53]

Patchset #2 (id:20001) has been deleted

[Fady Samuel, 2015-02-23 23:42:57]

The CQ bit was checked by fsamuel@chromium.org

[commit-bot: I haz the power, 2015-02-23 23:52:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/954543002/1

[commit-bot: I haz the power, 2015-02-23 23:55:24]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-23 23:55:56]

Patchset 1 (id:??) landed as
https://crrev.com/cab37f85ed91c494e86fc201bf1550b9ba467471
Cr-Commit-Position: refs/heads/master@{#317682}