Decouple WebViewImpl from WebView attributes

Decouple WebViewImpl from WebView attributes

Ideally web_view.js show know as little as possible about the internals of
WebView attributes and vice versa. This will allow WebView attributes to
eventually become GuestView attributes that can be shared with other GuestViewContainer
types.

This CL takes us in that direction by plumbing attach/detach into attributes which can
then decide how to respond to those events.

BUG=none
TBR=lazyboy@chromium.org

Committed: https://crrev.com/b2ff547e446523ba3b253a6fd9f1b3920f1f9632
Cr-Commit-Position: refs/heads/master@{#317744}

[Fady Samuel, 2015-02-23 19:14:23]

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

[paulmeyer, 2015-02-23 19:26:35]

LGTM! Nice style fixes too!

[Fady Samuel, 2015-02-23 19:39:15]

The CQ bit was checked by fsamuel@chromium.org

[commit-bot: I haz the power, 2015-02-23 19:40:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/950963002/1

[commit-bot: I haz the power, 2015-02-23 19:40:59]

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

[commit-bot: I haz the power, 2015-02-23 19:41:00]

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, 2015-02-23 19:41:51]

The CQ bit was checked by fsamuel@chromium.org

[commit-bot: I haz the power, 2015-02-23 19:43:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/950963002/1

[commit-bot: I haz the power, 2015-02-23 23:48:31]

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

[commit-bot: I haz the power, 2015-02-23 23:48:32]

Try jobs failed on following builders:
  linux_chromium_chromeos_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[Fady Samuel, 2015-02-24 01:24:00]

The CQ bit was checked by fsamuel@chromium.org

[Fady Samuel, 2015-02-24 01:24:00]

The patchset sent to the CQ was uploaded after l-g-t-m from
paulmeyer@chromium.org
Link to the patchset: https://codereview.chromium.org/950963002/#ps20001 (title:
"Fixed broken test")

[commit-bot: I haz the power, 2015-02-24 01:25:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/950963002/20001

[commit-bot: I haz the power, 2015-02-24 02:22:31]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-02-24 02:25:25]

Patchset 2 (id:??) landed as
https://crrev.com/b2ff547e446523ba3b253a6fd9f1b3920f1f9632
Cr-Commit-Position: refs/heads/master@{#317744}