DevTools: move FileSystemMapping from Workspace to Persistence

DevTools: move FileSystemMapping from Workspace to Persistence

This patch moves the FileSystemMapping under the persistence/ module.
This is along the plan which is outlined in the tracking bug.

Two things to note here:
- The FileSystemMapping object is still a singleton, some tests rely on
  this
- The patch addes a dependency from settings/ to persistence/. Ideally,
  we should make settings/ extendable via the Runtime, but that's a
  different story.

BUG=649837

[lushnikov, 2016-11-29 00:32:41]

Description was changed from

==========
DevTools: move FileSystemMapping from Workspace to Persistence

Following the trend, this patch moves FileSystemMapping from Workspace
module into Persistence module.

BUG=649837
==========

to

==========
DevTools: move FileSystemMapping from Workspace to Persistence

This patch moves the FileSystemMapping under the persistence/ module.
This is along the plan which is outlined in the tracking bug.

Two things to note here:
- The FileSystemMapping object is still a singleton, some tests rely on
  this
- The patch addes a dependency from settings/ to persistence/. Ideally,
  we should make settings/ extendable via the Runtime, but that's a
  different story.

BUG=649837
==========

[lushnikov, 2016-11-29 00:32:41]

lushnikov@chromium.org changed reviewers:
+ dgozman@chromium.org

[lushnikov, 2016-11-29 00:32:50]

please, take a look

[lushnikov, 2016-11-29 00:33:09]

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

[commit-bot: I haz the power, 2016-11-29 00:34:41]

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, 2016-11-29 02:49:43]

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

[commit-bot: I haz the power, 2016-11-29 02:49:44]

Dry run: This issue passed the CQ dry run.