Enable global (cross-application) drag/drop

Also adds a new flag constant, View.DRAG_FLAG_GLOBAL, which indicates that
the drag operation should be allowed to propagate the drag outside the
originating app.  When this flag is specified, all visible windows will
be notified about the ongoing drag.

Bug 3322724

Change-Id: Iaa3412a97f83f4e763019c9a03b5f09ebf75453f
diff --git a/core/java/android/view/View.java b/core/java/android/view/View.java
index 7536be1..7e968d7 100644
--- a/core/java/android/view/View.java
+++ b/core/java/android/view/View.java
@@ -2183,8 +2183,10 @@
     boolean mCanAcceptDrop;
 
     /**
-     * Flag indicating that a drag can cross window boundaries
-     * @hide
+     * Flag indicating that a drag can cross window boundaries.  When
+     * {@link #startDrag(ClipData, DragShadowBuilder, Object, int)} is called
+     * with this flag set, all visible applications will be able to participate
+     * in the drag operation and receive the dragged content.
      */
     public static final int DRAG_FLAG_GLOBAL = 1;