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

services/ui/ws/window_tree.cc

 // 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.
 
 #include "services/ui/ws/window_tree.h"
 
 #include <stddef.h>
 
 #include <utility>
 
@@ skipping 1348 matching lines @@
   ServerWindow* window =
       GetWindowByClientId(ClientWindowId(transport_window_id));
   if (!window || !access_policy_->CanSetClientArea(window))
     return;
 
   std::vector<gfx::Rect> additional_client_areas =
       transport_additional_client_areas.To<std::vector<gfx::Rect>>();
   window->SetClientArea(insets, additional_client_areas);
 }
 
-void WindowTree::SetHitTestMask(Id transport_window_id, const gfx::Rect& mask) {
+void WindowTree::SetHitTestMask(Id transport_window_id,
+                                const base::Optional<gfx::Rect>& mask) {
   ServerWindow* window =
       GetWindowByClientId(ClientWindowId(transport_window_id));
   if (!window || !access_policy_->CanSetHitTestMask(window)) {
     DVLOG(1) << "SetHitTestMask failed";
     return;
   }
 
-  if (!mask.IsEmpty())
-    window->SetHitTestMask(mask);
+  if (mask)
+    window->SetHitTestMask(*mask);
   else
     window->ClearHitTestMask();
 }
 
 void WindowTree::Embed(Id transport_window_id,
                        mojom::WindowTreeClientPtr client,
                        uint32_t flags,
                        const EmbedCallback& callback) {
   callback.Run(
       Embed(ClientWindowId(transport_window_id), std::move(client), flags));
@@ skipping 280 matching lines @@
 }
 
 bool WindowTree::IsWindowRootOfAnotherTreeForAccessPolicy(
     const ServerWindow* window) const {
   WindowTree* tree = window_server_->GetTreeWithRoot(window);
   return tree && tree != this;
 }
 
 }  // namespace ws
 }  // namespace ui