Avoid changing |drag_reverted_| if the drag was already completed on ChromeOS

ash/wm/toplevel_window_event_handler.h

Index: ash/wm/toplevel_window_event_handler.h
diff --git a/ash/wm/toplevel_window_event_handler.h b/ash/wm/toplevel_window_event_handler.h
index 5d9caf88526c53c16ecebb03205b9dc623e38c32..246b042dedb00fc89ceb18f94e6d8200b144a8c8 100644
--- a/ash/wm/toplevel_window_event_handler.h
+++ b/ash/wm/toplevel_window_event_handler.h
@@ -58,7 +58,12 @@ class ASH_EXPORT ToplevelWindowEventHandler
 
   enum DragCompletionStatus {
     DRAG_COMPLETE,
-    DRAG_REVERT
+    DRAG_REVERT,
+
+    // To be used when WindowResizer::GetTarget() is destroyed. Neither
+    // completes nor reverts the drag because both access the WindowResizer's
+    // window.
+    DRAG_RESIZER_WINDOW_DESTROYED
   };
 
   // Attempts to start a drag if one is not already in progress. Returns true if
@@ -68,8 +73,9 @@ class ASH_EXPORT ToplevelWindowEventHandler
                           int window_component,
                           aura::client::WindowMoveSource source);
 
-  // Finishes the drag.
-  void CompleteDrag(DragCompletionStatus status);
+  // Completes or reverts the drag if one is in progress. Returns true if a
+  // drag was completed or reverted.
+  bool CompleteDrag(DragCompletionStatus status);
 
   void HandleMousePressed(aura::Window* target, ui::MouseEvent* event);
   void HandleMouseReleased(aura::Window* target, ui::MouseEvent* event);