Make WindowManagerService.SettingsObserver multiuser-aware.

WindowManagerService.SettingsObserver has been used to monitor
per-user settings hence we have to take care of multiuser
scenario.

So far it's acceptable to monitor settings changes for all the
users because following event handlers are already
multiuser-aware.
- WindowManagerService#updateShowImeWithHardKeyboard
- WindowManagerService#updateCircularDisplayMaskIfNeeded

Bug: 21766030
Change-Id: I1d93095965c852ff90d8c7cc031c4755856a7e41

services/core/java/com/android/server/wm/WindowManagerService.java

@@ -577,8 +577,10 @@ public class WindowManagerService extends IWindowManager.Stub
         public SettingsObserver() {
             super(new Handler());
             ContentResolver resolver = mContext.getContentResolver();
-            resolver.registerContentObserver(mShowImeWithHardKeyboardUri, false, this);
-            resolver.registerContentObserver(mDisplayInversionEnabledUri, false, this);
+            resolver.registerContentObserver(mShowImeWithHardKeyboardUri, false, this,
+                    UserHandle.USER_ALL);
+            resolver.registerContentObserver(mDisplayInversionEnabledUri, false, this,
+                    UserHandle.USER_ALL);
         }
 
         @Override