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

services/ui/public/cpp/lib/window_tree_client.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/public/cpp/window_tree_client.h"
 
 #include <stddef.h>
 
 #include <string>
 #include <utility>
@@ skipping 263 matching lines @@
   tree_->SetClientArea(window_id, client_area, additional_client_areas);
 }
 
 void WindowTreeClient::SetHitTestMask(Id window_id, const gfx::Rect& mask) {
   DCHECK(tree_);
   tree_->SetHitTestMask(window_id, mask);
 }
 
 void WindowTreeClient::ClearHitTestMask(Id window_id) {
   DCHECK(tree_);
-  tree_->SetHitTestMask(window_id, {});
+  tree_->SetHitTestMask(window_id, base::nullopt);
 }
 
 void WindowTreeClient::SetFocus(Window* window) {
   // In order for us to get here we had to have exposed a window, which implies
   // we got a client.
   DCHECK(tree_);
   const uint32_t change_id = ScheduleInFlightChange(
       base::WrapUnique(new InFlightFocusChange(this, focused_window_)));
   tree_->SetFocus(change_id, window ? server_id(window) : 0);
   LocalSetFocus(window);
@@ skipping 955 matching lines @@
     Window* window,
     const gfx::Vector2d& offset,
     const gfx::Insets& hit_area) {
   if (window_manager_internal_client_) {
     window_manager_internal_client_->SetUnderlaySurfaceOffsetAndExtendedHitArea(
         server_id(window), offset.x(), offset.y(), hit_area);
   }
 }
 
 }  // namespace ui