mus: Implement interwindow drag and drop

services/ui/ws/event_dispatcher.h

Index: services/ui/ws/event_dispatcher.h
diff --git a/services/ui/ws/event_dispatcher.h b/services/ui/ws/event_dispatcher.h
index aeeffd0a90a6b13ab0730e7c3815ce92c782877c..b410f58a05c5d4e8b548d93be8dc5ceba005220a 100644
--- a/services/ui/ws/event_dispatcher.h
+++ b/services/ui/ws/event_dispatcher.h
@@ -14,6 +14,7 @@
 #include "base/macros.h"
 #include "services/ui/common/types.h"
 #include "services/ui/public/interfaces/event_matcher.mojom.h"
+#include "services/ui/ws/current_drag_operation_delegate.h"
 #include "services/ui/ws/modal_window_controller.h"
 #include "services/ui/ws/server_window_observer.h"
 #include "ui/gfx/geometry/rect_f.h"
@@ -26,15 +27,18 @@ class LocatedEvent;
 namespace ws {
 
 class Accelerator;
+class CurrentDragOperation;
 class EventDispatcherDelegate;
 class ServerWindow;
+class WindowTree;
 
 namespace test {
 class EventDispatcherTestApi;
 }
 
 // Handles dispatching events to the right location as well as updating focus.
-class EventDispatcher : public ServerWindowObserver {
+class EventDispatcher : public ServerWindowObserver,
+                        public CurrentDragOperationDelegate {
  public:
   enum class AcceleratorMatchPhase {
     // Both pre and post should be considered.
@@ -75,6 +79,14 @@ class EventDispatcher : public ServerWindowObserver {
     return capture_window_client_id_;
   }
 
+  // TODO(erg): Am I not supposed to pass window_tree here?
+  void SetDragDropSourceWindow(

[sky, 2016/08/24 00:08:57]

I recommend having this take an interface rather than WindowTree. WindowTree
either implements the interface, or creates an object that implements the
interface (probably the former).
As far as lifetime issues, WindowTree will know it's installed itself as the
drag drop source, right? It can cancel dnd from the destructor (or sooner) as
necessary.

+      uint32_t change_id,
+      WindowTree* window_tree,
+      ServerWindow* capture_window,
+      mojo::Map<mojo::String, mojo::Array<uint8_t>> mime_data,
+      uint32_t drag_operations);
+
   // Adds a system modal window. The window remains modal to system until it is
   // destroyed. There can exist multiple system modal windows, in which case the
   // one that is visible and added most recently or shown most recently would be
@@ -117,6 +129,8 @@ class EventDispatcher : public ServerWindowObserver {
   // handled this is again called with an AcceleratorMatchPhase of POST_ONLY.
   void ProcessEvent(const ui::Event& event, AcceleratorMatchPhase match_phase);
 
+  ServerWindow* FindDeepestVisibleWindowForEvents(gfx::Point* location);
+
  private:
   friend class test::EventDispatcherTestApi;
 
@@ -202,8 +216,6 @@ class EventDispatcher : public ServerWindowObserver {
   Accelerator* FindAccelerator(const ui::KeyEvent& event,
                                const ui::mojom::AcceleratorPhase phase);
 
-  ServerWindow* FindDeepestVisibleWindowForEvents(gfx::Point* location);
-
   // ServerWindowObserver:
   void OnWillChangeWindowHierarchy(ServerWindow* window,
                                    ServerWindow* new_parent,
@@ -211,11 +223,16 @@ class EventDispatcher : public ServerWindowObserver {
   void OnWindowVisibilityChanged(ServerWindow* window) override;
   void OnWindowDestroyed(ServerWindow* window) override;
 
+  // CurrentDragOperationDelegate:
+  void OnDragOver(bool success) override;
+
   EventDispatcherDelegate* delegate_;
 
   ServerWindow* capture_window_;
   ClientSpecificId capture_window_client_id_;
 
+  std::unique_ptr<CurrentDragOperation> current_drag_drop_operation_;
+
   ModalWindowController modal_window_controller_;
 
   bool mouse_button_down_;