Reland: [IndexedDB] Delete callbacks state on worker thread exit.

Reland: [IndexedDB] Delete callbacks state on worker thread exit.

During refactoring of r430110 the logic to actually delete the internal
state of IndexedDBCallbacksImpl and IndexedDBDatabaseCallbacksImpl
objects that lives on worker threads was accidentally removed.

This reland will fix the DCHECK encountered when actually exercising
this deletion path.

BUG=667465
Review-Url: https://codereview.chromium.org/2524823002
Cr-Commit-Position: refs/heads/master@{#434030}
(cherry picked from commit 6d1044b605d7dfa073437e09fd966f306137a0c9)

Committed: https://chromium.googlesource.com/chromium/src/+/c5646073b3867c4b59a83a502bad6ba5681816d8

[Reilly Grant (use Gerrit), 2016-11-23 18:58:49]

Description was changed from

==========
Reland: [IndexedDB] Delete callbacks state on worker thread exit.

During refactoring of r430110 the logic to actually delete the internal
state of IndexedDBCallbacksImpl and IndexedDBDatabaseCallbacksImpl
objects that lives on worker threads was accidentally removed.

This reland will fix the DCHECK encountered when actually exercising
this deletion path.

BUG=667465

Review-Url: https://codereview.chromium.org/2524823002
Cr-Commit-Position: refs/heads/master@{#434030}
(cherry picked from commit 6d1044b605d7dfa073437e09fd966f306137a0c9)
==========

to

==========
Reland: [IndexedDB] Delete callbacks state on worker thread exit.

During refactoring of r430110 the logic to actually delete the internal
state of IndexedDBCallbacksImpl and IndexedDBDatabaseCallbacksImpl
objects that lives on worker threads was accidentally removed.

This reland will fix the DCHECK encountered when actually exercising
this deletion path.

BUG=667465

Review-Url: https://codereview.chromium.org/2524823002
Cr-Commit-Position: refs/heads/master@{#434030}
(cherry picked from commit 6d1044b605d7dfa073437e09fd966f306137a0c9)

Committed:
https://chromium.googlesource.com/chromium/src/+/c5646073b3867c4b59a83a502bad...
==========

[Reilly Grant (use Gerrit), 2016-11-23 18:58:50]

Committed patchset #1 (id:1) manually as
c5646073b3867c4b59a83a502bad6ba5681816d8.