MDM Download Restriction support

This commit adds MDM management of the following if the restriction
is enabled via the MDM mechanism:
    1. The ability to download.
    2. The download directory under '/Phone Storage/', if
       downloading is permitted.

These restrictions are only effective on SWE provisioned in the
'Work' profile. Non-work-profile SWE will not be affected.

When the download capability has been restricted, clicking a download
link results in a Toast message (Managed by your administrator). A long-press
of the link still brings up a context menu, but the 'Save link as' menuitem
is disabled in this case.

If MDM sets the download directory, it is not setting the full path, just
the directory under '/Phone Storage'. The directory specified must include
a leading '/' i.e. '/NewDownloadDir'.

Change-Id: I13a44892a36925d6324b87f7655d79fb0776f8a9
diff --git a/src/com/android/browser/BrowserSettings.java b/src/com/android/browser/BrowserSettings.java
index 04da119..6ee8e29 100644
--- a/src/com/android/browser/BrowserSettings.java
+++ b/src/com/android/browser/BrowserSettings.java
@@ -34,6 +34,7 @@
 import com.android.browser.mdm.AutoFillRestriction;
 import com.android.browser.mdm.DevToolsRestriction;
 import com.android.browser.mdm.DoNotTrackRestriction;
+import com.android.browser.mdm.DownloadDirRestriction;
 import com.android.browser.mdm.EditBookmarksRestriction;
 import com.android.browser.mdm.IncognitoRestriction;
 import com.android.browser.mdm.ManagedBookmarksRestriction;
@@ -187,6 +188,7 @@
         AutoFillRestriction.getInstance();
         DevToolsRestriction.getInstance();
         DoNotTrackRestriction.getInstance();
+        DownloadDirRestriction.getInstance();
         EditBookmarksRestriction.getInstance();
         IncognitoRestriction.getInstance();
         ManagedBookmarksRestriction.getInstance();