Updating DropShadow as drag and drop hovers over views.

Also moved DragShadowBuilder to Activity level (needs constant reference
to it).

Bug: 31182423
Change-Id: Id3a09cff863d529f92e15e23c6cf53a2ca9da20d
diff --git a/src/com/android/documentsui/DrawerController.java b/src/com/android/documentsui/DrawerController.java
index d5b8f4f..f8062a7 100644
--- a/src/com/android/documentsui/DrawerController.java
+++ b/src/com/android/documentsui/DrawerController.java
@@ -160,7 +160,7 @@
         }
 
         @Override
-        public void onDragEntered(View v) {
+        public void onDragEntered(View v, Object localState) {
             assert (v.getId() == R.id.drawer_edge);
 
             setOpen(true);