Mojo C++ bindings: support mapping T and T? differently.

services/ui/public/interfaces/window_tree.mojom

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module ui.mojom;
 
 import "cc/ipc/surface_id.mojom";
 import "services/ui/public/interfaces/cursor.mojom";
 import "services/ui/public/interfaces/event_matcher.mojom";
 import "services/ui/public/interfaces/mus_constants.mojom";
@@ skipping 84 matching lines @@
 
   // Sets the client area of the specified window. The client area is specified
   // by way of insets. Everything outside of the insets, and not in
   // |additional_client_areas| is considered non-client area.
   // TODO(sky): convert additional_client_areas to a path.
   SetClientArea(uint32 window_id,
                 gfx.mojom.Insets insets,
                 array<gfx.mojom.Rect>? additional_client_areas);
 
   // Mouse events outside a hit test mask do not hit the window. The |mask| is
-  // in window local coordinates. Pass null to clear the mask.
+  // in window local coordinates. Pass an empty rect to clear the mask.
   // TODO(jamescook): Convert |mask| to a path. http://crbug.com/613210
-  SetHitTestMask(uint32 window_id, gfx.mojom.Rect? mask);
+  SetHitTestMask(uint32 window_id, gfx.mojom.Rect mask);

[sky, 2016/07/26 21:26:16]

We want to allow null here too.

[yzshen1, 2016/07/26 21:32:36]

Please see my comment for the other place.

 
   // 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.
   SetWindowVisibility(uint32 change_id, uint32 window_id, bool visible);
 
   // Sets an individual named property. Setting an individual property to null
   // deletes the property.
   SetWindowProperty(uint32 change_id,
                     uint32 window_id,
@@ skipping 281 matching lines @@
   // See description of WindowManager for details.
   GetWindowManager(associated WindowManager& internal);
 };
 
 // Mus provides this interface as a way for clients to connect and obtain a
 // WindowTree handle with a supplied WindowTreeClient handle. The
 // WindowTreeClient has no roots, use NewTopLevelWindow() to create one.
 interface WindowTreeFactory {
   CreateWindowTree(WindowTree& tree_request, WindowTreeClient client);
 };