aura-mus: add a drag representation image.

ash/mus/window_manager.h

Index: ash/mus/window_manager.h
diff --git a/ash/mus/window_manager.h b/ash/mus/window_manager.h
index 2c58abe2fcb910c4c85b72cfc70a11f33f4130da..328dfd42b42a43b5196119ae22338740a9525998 100644
--- a/ash/mus/window_manager.h
+++ b/ash/mus/window_manager.h
@@ -41,6 +41,7 @@ class WMState;
 
 namespace ash {
 
+class DragImageView;
 class RootWindowController;
 class ScreenMus;
 class ShellDelegate;
@@ -151,6 +152,12 @@ class WindowManager : public aura::WindowManagerDelegate,
       std::map<std::string, std::vector<uint8_t>>* properties) override;
   void OnWmClientJankinessChanged(const std::set<aura::Window*>& client_windows,
                                   bool not_responding) override;
+  void OnWmBuildDragImage(const gfx::Point& cursor_location,
+                          const SkBitmap& drag_image,
+                          const gfx::Vector2d& drag_image_offset,
+                          ui::mojom::DragEventSource source) override;
+  void OnWmMoveDragImage(const gfx::Point& cursor_location) override;
+  void OnWmDestroyDragImage() override;
   void OnWmWillCreateDisplay(const display::Display& display) override;
   void OnWmNewDisplay(std::unique_ptr<aura::WindowTreeHostMus> window_tree_host,
                       const display::Display& display) override;
@@ -203,6 +210,13 @@ class WindowManager : public aura::WindowManagerDelegate,
   // See WmShellMus's constructor for details. Tests may set to false.
   bool create_session_state_delegate_stub_for_test_ = true;
 
+  // An image representation of the contents of the current drag and drop

[sky, 2017/03/23 00:05:36]

Please put the drag related state into a struct. That way it's clear what state
is related to a drag.

[Elliot Glaysher, 2017/03/23 19:58:44]

Done.

+  // clipboard.
+  std::unique_ptr<ash::DragImageView> drag_image_;
+
+  // The cursor offset of the dragged item.
+  gfx::Vector2d drag_image_offset_;
+
   DISALLOW_COPY_AND_ASSIGN(WindowManager);
 };