mus: Implement interwindow drag and drop

services/ui/public/interfaces/window_tree.mojom

Index: services/ui/public/interfaces/window_tree.mojom
diff --git a/services/ui/public/interfaces/window_tree.mojom b/services/ui/public/interfaces/window_tree.mojom
index 5adcca21706011d8fa3405bc58ed6ff48fa7a4b2..1f191581723c33be641b9aabf9f0f91418062013 100644
--- a/services/ui/public/interfaces/window_tree.mojom
+++ b/services/ui/public/interfaces/window_tree.mojom
@@ -12,6 +12,7 @@ import "services/ui/public/interfaces/surface.mojom";
 import "services/ui/public/interfaces/window_manager.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/events/mojo/event.mojom";
 import "ui/gfx/geometry/mojo/geometry.mojom";
 import "ui/platform_window/mojo/text_input_state.mojom";
@@ -113,6 +114,11 @@ interface WindowTree {
   // TODO(jamescook): Convert |mask| to a path. http://crbug.com/613210
   SetHitTestMask(uint32 window_id, gfx.mojom.Rect? mask);
 
+  // Called by clients that want to accept drags. Windows default
+  // to this being disabled; a window must actively opt-in to
+  // receiving Drag*() calls.
+  SetCanAcceptDrags(uint32 window_id, bool accepts_drags);
+
   // Sets the visibility of the specified window to |visible|. Connections are
   // allowed to change the visibility of any window they have created, as well
   // as any of their roots.
@@ -270,6 +276,20 @@ interface WindowTree {
   // Tells the window manager to cancel any in progress window move started with
   // StartWindowMove() and to revert the window bounds to how they were.
   CancelWindowMove(uint32 window_id);
+
+  // Called by the client to start a drag operation.
+  //
+  // This will cause the window server to create a window with
+  // |drag_representation| and start processing events for drag and
+  // drop. It will set the clipboard’s DRAG clipboard to |drag_data|
+  // (this is part of this interface since mojom.Clipboard is usually
+  // on a different pipe).
+  PerformDragDrop(uint32 change_id,
+                  uint32 source_window_id,
+                  map<string, array<uint8>> drag_data,
+                  uint32 drag_operation,
+                  gfx.mojom.Point cursor_location,
+                  skia.mojom.Bitmap drag_representation);
 };
 
 // Changes to windows are not sent to the connection that originated the
@@ -400,6 +420,35 @@ interface WindowTreeClient {
 
   OnWindowPredefinedCursorChanged(uint32 window_id, Cursor cursor_id);
 
+  // Called when the mouse cursor enters a window that has opted into
+  // accepting drags through SetAcceptsDrags(), providing a list
+  // of available mime types.  Returns a bitmask of the supported
+  // operations.
+  OnDragEnter(uint32 window,
+              map<string, array<uint8>> drag_data,
+              uint32 key_state,
+              gfx.mojom.Point position,
+              uint32 effect_bitmask) => (uint32 supported_op_bitmask);
+
+  // Called when the pointer moves over the window after the initial
+  // DragEnter. Returns a bitmask of the supported operations at this
+  // location.
+  OnDragOver(uint32 window,
+             uint32 key_state,
+             gfx.mojom.Point position,
+             uint32 effect_bitmask) => (uint32 supported_op_bitmask);
+
+  // Called when the pointer leaves a window or if the drop is
+  // canceled.
+  OnDragLeave(uint32 window);
+
+  // Called when the drop occurs on a window. Returns the action
+  // taken.
+  OnDragDrop(uint32 window,
+             uint32 key_state,
+             gfx.mojom.Point position,
+             uint32 effect_bitmask) => (uint32 effect_taken);
+
   // A change initiated from the client has completed. See description of
   // change ids for details.
   OnChangeCompleted(uint32 change_id, bool success);