Files.app: Add private API functions for the multi-profile support.

This CL adds two file browser private API functions.
The getProfiles function obtains a current logged-in profiles.
The visitDesktop function moves the current window to the given user's desktop.

BUG=336086
TEST=call the APIs from the inspector.

Review URL: https://codereview.chromium.org/132693027

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247196 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247196