mus: Implement interwindow drag and drop

services/ui/public/cpp/in_flight_change.h

Index: services/ui/public/cpp/in_flight_change.h
diff --git a/services/ui/public/cpp/in_flight_change.h b/services/ui/public/cpp/in_flight_change.h
index 7981ef2f71ccbe82e8f09a7499495ebd53256af4..649aa542340fe297a7d760d563d8f9ba0b014692 100644
--- a/services/ui/public/cpp/in_flight_change.h
+++ b/services/ui/public/cpp/in_flight_change.h
@@ -32,6 +32,7 @@ enum class ChangeType {
   BOUNDS,
   CAPTURE,
   DELETE_WINDOW,
+  DRAG_LOOP,
   FOCUS,
   MOVE_LOOP,
   NEW_TOP_LEVEL_WINDOW,
@@ -144,16 +145,16 @@ class InFlightBoundsChange : public InFlightChange {
   DISALLOW_COPY_AND_ASSIGN(InFlightBoundsChange);
 };
 
-class InFlightMoveLoopChange : public InFlightChange {
+class InFlightDragChange : public InFlightChange {
  public:
-  explicit InFlightMoveLoopChange(Window* window);
+  InFlightDragChange(Window* window, ChangeType type);
 
   // InFlightChange:
   void SetRevertValueFrom(const InFlightChange& change) override;
   void Revert() override;
 
  private:
-  DISALLOW_COPY_AND_ASSIGN(InFlightMoveLoopChange);
+  DISALLOW_COPY_AND_ASSIGN(InFlightDragChange);
 };
 
 // Inflight change that crashes on failure. This is useful for changes that are