Deprecate FileSystemMountPointProvider::GetFileSystemRootPathOnFileThread

Deprecate FileSystemMountPointProvider::GetFileSystemRootPathOnFileThread

This was initially introduced to get ExternalFileSystem's
local mount root path, but accessing MountPointProvider
from lower-layer FileUtil module looks ugly.

This patch:
- Deprecate FileSystemMountPointProvider::GetFileSystemRootPathOnFileThread
- Add FileSystemOperationContext::root_path() instead for passing root path

BUG=241701
TEST=Moved tests from content_unittests:FileSystemMountPointProviderTest.*
 to content_unittests:SandboxMountPointProviderTest.*

R=bauerb@chromium.org, michaeln@chromium.org, tzik@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=202776

[kinuko, 2013-05-24 13:04:20]

PTL

[tzik, 2013-05-27 08:26:52]

lgtm

[kinuko, 2013-05-27 08:39:46]

mkwst@: can you do OWNER review for chrome/browser/browsing_data change?

[kinuko, 2013-05-27 10:32:24]

On 2013/05/27 08:39:46, kinuko wrote:
> mkwst@: can you do OWNER review for chrome/browser/browsing_data change?

Or michaeln@, for chrome/browser/browsing_data change. Thx,

(Also cc-ing some related folks)

[kinuko, 2013-05-28 14:43:51]

bauerb@: can you do OWNER review for chrome/browser/browsing_data change?

[Bernhard Bauer, 2013-05-28 16:03:10]

LGTM! (Feel free to TBR signature updates like these).

[michaeln, 2013-05-28 19:05:35]

chrome/browser lgtm

[commit-bot: I haz the power, 2013-05-29 02:34:41]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/kinuko@chromium.org/15959006/21001

[commit-bot: I haz the power, 2013-05-29 03:07:05]

Step "update" is always a major failure.
Look at the try server FAQ for more details.
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_rel&...

[kinuko, 2013-05-29 04:25:11]

Committed patchset #2 manually as r202776 (presubmit successful).