[Extensions] Fix bookmark drag-and-drop bug

[Extensions] Fix bookmark drag-and-drop bug

https://crrev.com/a32a0900c104b2143e6462febc81e6900dbd2104 stopped
ExtensionWebUI from being created for chrome://bookmarks in favor of
a WebContentsUserData implementation. Unfortunately, WebUI is created
on a per render frame basis and refreshed on navigation, whereas
WebContentsUserData are created once at web contents initalization.
As such, the bookmarks drag helper wasn't being created.

Instead, just create the bookmarks drag helper for each web contents.
It's a little unfortunate, but it's only called into with explicit
bookmark drag-and-drop commands and doesn't have any real initialization
cost or maintained state, so if it's never used in the web contents, it
becomes essentially a no-op. In practice, this is probably cheaper than
watching each navigation and conditionally creating/destroying the
helper on the fly.

BUG=665411
Committed: https://crrev.com/5b68b9b08166d20070c7360c11da97e75f547f3d
Cr-Commit-Position: refs/heads/master@{#432978}

[Devlin, 2016-11-17 18:38:32]

The CQ bit was checked by rdevlin.cronin@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-11-17 18:39:29]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-11-17 19:42:31]

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

[commit-bot: I haz the power, 2016-11-17 19:42:32]

Dry run: This issue passed the CQ dry run.

[Devlin, 2016-11-17 19:44:51]

rdevlin.cronin@chromium.org changed reviewers:
+ asargent@chromium.org

[Devlin, 2016-11-17 19:44:52]

Antony, mind taking a look?

[asargent_no_longer_on_chrome, 2016-11-17 20:14:35]

lgtm

[Devlin, 2016-11-17 20:59:38]

The CQ bit was checked by rdevlin.cronin@chromium.org

[commit-bot: I haz the power, 2016-11-17 21:00:46]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-11-17 21:49:21]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-11-17 21:51:53]

Description was changed from

==========
[Extensions] Fix bookmark drag-and-drop bug

https://crrev.com/a32a0900c104b2143e6462febc81e6900dbd2104 stopped
ExtensionWebUI from being created for chrome://bookmarks in favor of
a WebContentsUserData implementation. Unfortunately, WebUI is created
on a per render frame basis and refreshed on navigation, whereas
WebContentsUserData are created once at web contents initalization.
As such, the bookmarks drag helper wasn't being created.

Instead, just create the bookmarks drag helper for each web contents.
It's a little unfortunate, but it's only called into with explicit
bookmark drag-and-drop commands and doesn't have any real initialization
cost or maintained state, so if it's never used in the web contents, it
becomes essentially a no-op. In practice, this is probably cheaper than
watching each navigation and conditionally creating/destroying the
helper on the fly.

BUG=665411
==========

to

==========
[Extensions] Fix bookmark drag-and-drop bug

https://crrev.com/a32a0900c104b2143e6462febc81e6900dbd2104 stopped
ExtensionWebUI from being created for chrome://bookmarks in favor of
a WebContentsUserData implementation. Unfortunately, WebUI is created
on a per render frame basis and refreshed on navigation, whereas
WebContentsUserData are created once at web contents initalization.
As such, the bookmarks drag helper wasn't being created.

Instead, just create the bookmarks drag helper for each web contents.
It's a little unfortunate, but it's only called into with explicit
bookmark drag-and-drop commands and doesn't have any real initialization
cost or maintained state, so if it's never used in the web contents, it
becomes essentially a no-op. In practice, this is probably cheaper than
watching each navigation and conditionally creating/destroying the
helper on the fly.

BUG=665411

Committed: https://crrev.com/5b68b9b08166d20070c7360c11da97e75f547f3d
Cr-Commit-Position: refs/heads/master@{#432978}
==========

[commit-bot: I haz the power, 2016-11-17 21:51:54]

Patchset 1 (id:??) landed as
https://crrev.com/5b68b9b08166d20070c7360c11da97e75f547f3d
Cr-Commit-Position: refs/heads/master@{#432978}