Disable cross-app drag/drop

@hides the View constant that designates a drag as cross-app, and also
forcibly ignores that flag on the system_server side even if it's passed
to startDrag() as a literal.

Change-Id: I6f321bdf0389db5bb44131fd0f8d6b92f049be52
diff --git a/services/java/com/android/server/WindowManagerService.java b/services/java/com/android/server/WindowManagerService.java
index b7a276f..b662c55 100644
--- a/services/java/com/android/server/WindowManagerService.java
+++ b/services/java/com/android/server/WindowManagerService.java
@@ -5889,7 +5889,7 @@
                         outSurface.copyFrom(surface);
                         final IBinder winBinder = window.asBinder();
                         token = new Binder();
-                        mDragState = new DragState(token, surface, flags, winBinder);
+                        mDragState = new DragState(token, surface, /*flags*/ 0, winBinder);
                         mDragState.mSurface = surface;
                         token = mDragState.mToken = new Binder();