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..3a6c5e77b04aef02a112c09b4c9cd390bfb79da5 100644
--- a/services/ui/public/interfaces/window_manager.mojom
+++ b/services/ui/public/interfaces/window_manager.mojom
@@ -9,9 +9,11 @@ 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";
+import "ui/events/mojo/event_constants.mojom";
 import "ui/gfx/geometry/mojo/geometry.mojom";
 
 // WindowManager is used when a WindowTreeClient attempts to modify
@@ -189,6 +191,23 @@ 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 representation.
+  //
+  // TODO(erg): SkBitmap is the wrong data type for the drag image; we should
+  // be passing ImageSkias once http://crbug.com/655874 is implemented.
+  WmBuildDragImage(gfx.mojom.Point screen_location,
+                   skia.mojom.Bitmap? drag_image,

[Tom Sepez, 2017/03/23 20:05:13]

So .. we're passing a skia bitmap up to a more-privileged process.  Is there a
precedent for this?  Thanks,

[Elliot Glaysher, 2017/03/23 20:24:20]

IIUC, the image decoder
(services/image_decoder/public/interfaces/image_decoder.mojom) takes a set of
raw bytes and hands back a skia.mojom.Bitmap. This service is run in a tight
sandbox and passes its data back to the browser process.

+                   gfx.mojom.Vector2d drag_image_offset,
+                   PointerKind source);
+
+  // Moves the drag representation image to |screen_location|. The window server
+  // queues further drags locally until they receive the callback.
+  WmMoveDragImage(gfx.mojom.Point screen_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().