👀 Cleanup DocumentMode migration helpers.

Cleanup DocumentMode migration helpers.

Remove DocumentMigrationHelper and DocumentModePreference. This helps
to remove many dependencies on TabPersistentStore's methods.

BUG=612245
Committed: https://crrev.com/5df8354b79028ebe02c4ac1ad911bc6e39037b8b
Cr-Commit-Position: refs/heads/master@{#394109}

[Peter Wen, 2016-05-16 20:04:05]

wnwen@chromium.org changed reviewers:
+ dfalcantara@chromium.org

[Peter Wen, 2016-05-16 20:04:06]

🎶 Let it go, let it go, the code never bothered me anyways (this is a lie). 🎶

[gone, 2016-05-16 20:10:46]

Baby 👣.  lgtm

[Peter Wen, 2016-05-17 12:59:57]

The CQ bit was checked by wnwen@chromium.org

[commit-bot: I haz the power, 2016-05-17 13:00:12]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1982043002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1982043002/1

[commit-bot: I haz the power, 2016-05-17 13:34:21]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-05-17 13:35:42]

Description was changed from

==========
Cleanup DocumentMode migration helpers.

Remove DocumentMigrationHelper and DocumentModePreference. This helps
to remove many dependencies on TabPersistentStore's methods.

BUG=612245
==========

to

==========
Cleanup DocumentMode migration helpers.

Remove DocumentMigrationHelper and DocumentModePreference. This helps
to remove many dependencies on TabPersistentStore's methods.

BUG=612245

Committed: https://crrev.com/5df8354b79028ebe02c4ac1ad911bc6e39037b8b
Cr-Commit-Position: refs/heads/master@{#394109}
==========

[commit-bot: I haz the power, 2016-05-17 13:35:43]

Patchset 1 (id:??) landed as
https://crrev.com/5df8354b79028ebe02c4ac1ad911bc6e39037b8b
Cr-Commit-Position: refs/heads/master@{#394109}