aura-mus: add a drag representation image.

services/ui/public/interfaces/window_manager.mojom

Index: services/ui/public/interfaces/window_manager.mojom
diff --git a/services/ui/public/interfaces/window_manager.mojom b/services/ui/public/interfaces/window_manager.mojom
index fd055b20442eb80d96f6f7ebad2bb7a99989daf8..ead0c0a1c441469eb2e1e8607f03b960abdaf835 100644
--- a/services/ui/public/interfaces/window_manager.mojom
+++ b/services/ui/public/interfaces/window_manager.mojom
@@ -9,6 +9,7 @@ import "services/ui/public/interfaces/cursor.mojom";
 import "services/ui/public/interfaces/event_matcher.mojom";
 import "services/ui/public/interfaces/window_manager_constants.mojom";
 import "services/ui/public/interfaces/window_tree_constants.mojom";
+import "skia/public/interfaces/bitmap.mojom";
 import "ui/base/mojo/ui_base_types.mojom";
 import "ui/display/mojo/display.mojom";
 import "ui/events/mojo/event.mojom";
@@ -189,6 +190,20 @@ interface WindowManager {
   // can update the UI for the janky windows.
   WmClientJankinessChanged(uint16 client_id, bool janky);
 
+  // Asks the WindowManager to create a drag representation window: a window
+  // which contains a single image represent

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

'representation.' ?

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

Done.

+  WmBuildDragImage(gfx.mojom.Point cursor_location,

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

cursor_location->screen_location (I'm assuming it's in screen coordinates).

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

Done.

+                   skia.mojom.Bitmap? drag_image,
+                   gfx.mojom.Vector2d drag_image_offset,
+                   DragEventSource source);
+
+  // Moves the drag representation image to |cursor_location|. Users should

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

'Users should' The window server queues ...

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

Done.

+  // queue further drags locally until they receive the callback.
+  WmMoveDragImage(gfx.mojom.Point cursor_location) => ();
+
+  // Called when the drag image is no longer needed.
+  WmDestroyDragImage();
+
   // Asks the WindowManager to interactively move the window. This will return
   // whether this completed successfully or not through the client's
   // OnWmMoveLoopCompleted().