Port IndexedDB open() and database callbacks to Mojo.

Port IndexedDB open() and database callbacks to Mojo.

This is the first of many changes that will migrate IndexedDB from
Chrome IPC to Mojo. We start with implementing DatabaseFactory::Open()
and the associated DatabaseClient interface used for sending database
events.

BUG=627484

[Reilly Grant (use Gerrit), 2016-09-09 23:32:21]

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

[commit-bot: I haz the power, 2016-09-09 23:33:11]

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

[Reilly Grant (use Gerrit), 2016-09-09 23:34:00]

reillyg@chromium.org changed reviewers:
+ cmumford@chromium.org, dcheng@chromium.org

[Reilly Grant (use Gerrit), 2016-09-09 23:34:01]

cmumford@, please review the change in general.
dcheng@, please review indexed_db.mojom and
indexed_db_database_error_struct_traits.h.

[commit-bot: I haz the power, 2016-09-09 23:37:00]

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

[commit-bot: I haz the power, 2016-09-09 23:37:01]

Dry run: Try jobs failed on following builders:
  chromium_presubmit on master.tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presub...)
  mac_chromium_compile_dbg_ng on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_comp...)
  mac_chromium_rel_ng on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

[Reilly Grant (use Gerrit), 2016-09-10 01:16:50]

Patchset #2 (id:20001) has been deleted

[Reilly Grant (use Gerrit), 2016-09-10 01:27:31]

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

[commit-bot: I haz the power, 2016-09-10 01:28:04]

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

[Reilly Grant (use Gerrit), 2016-09-10 01:28:12]

reillyg@chromium.org changed reviewers:
+ rockot@chromium.org

[Reilly Grant (use Gerrit), 2016-09-10 01:28:12]

rockot@, can you also take a general look to let me know if I'm using associated
interfaces correctly?

[commit-bot: I haz the power, 2016-09-10 01:54:17]

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

[commit-bot: I haz the power, 2016-09-10 01:54:19]

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

[haraken, 2016-09-12 01:01:49]

This CL looks amazing! Changes to WebKit/ generally look good.

[Ken Rockot(use gerrit already), 2016-09-12 20:52:37]

You appear to be using associated interfaces correctly. My only concern, since I
don't really know much about the code here, is that the old open implementation
sent an IPC via a ThreadSafeSender. Is it guaranteed that this is actually only
called from the main thread?

[Reilly Grant (use Gerrit), 2016-10-04 02:01:16]

Abandoning this CL as it changes too much too quickly and won't work from worker
threads. https://codereview.chromium.org/2370643004 is its replacement.