Reify view ownership as a message pipe.

services/ui/launcher/launcher_view_tree.h

 // Copyright 2015 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.
 
 #ifndef SERVICES_UI_LAUNCHER_VIEW_TREE_IMPL_H_
 #define SERVICES_UI_LAUNCHER_VIEW_TREE_IMPL_H_
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "mojo/public/cpp/bindings/binding.h"
 #include "mojo/services/gfx/composition/interfaces/compositor.mojom.h"
 #include "mojo/services/native_viewport/interfaces/native_viewport.mojom.h"
 #include "mojo/services/ui/input/interfaces/input_dispatcher.mojom.h"
 #include "mojo/services/ui/views/interfaces/view_manager.mojom.h"
 
 namespace launcher {
 
 class LauncherViewTree : public mojo::ui::ViewTree,
                          public mojo::gfx::composition::SceneListener {
  public:
   LauncherViewTree(mojo::gfx::composition::Compositor* compositor,
                    mojo::ui::ViewManager* view_manager,
                    mojo::ContextProviderPtr context_provider,
                    mojo::ViewportMetricsPtr viewport_metrics,
                    const base::Closure& shutdown_callback);
 
   ~LauncherViewTree() override;
 
-  void SetRoot(mojo::ui::ViewTokenPtr token);
+  void SetRoot(mojo::ui::ViewOwnerPtr owner);
   void SetViewportMetrics(mojo::ViewportMetricsPtr viewport_metrics);
   void DispatchEvent(mojo::EventPtr event);
 
  private:
   // |SceneListener|:
   void OnResourceUnavailable(
       uint32_t resource_id,
       const OnResourceUnavailableCallback& callback) override;
 
   // |ViewTree|:
   void OnLayout(const OnLayoutCallback& callback) override;
   void OnRootUnavailable(uint32_t root_key,
                          const OnRootUnavailableCallback& callback) override;
 
   void OnRendererConnectionError();
   void OnSceneConnectionError();
   void OnViewTreeConnectionError();
   void OnInputDispatcherConnectionError();
 
   void OnSceneRegistered(mojo::gfx::composition::SceneTokenPtr scene_token);
-  void OnViewTreeRegistered(mojo::ui::ViewTreeTokenPtr view_tree_token);
 
   void LayoutRoot();
   void OnLayoutResult(mojo::ui::ViewLayoutInfoPtr info);
 
   void SetRootScene();
 
   void PublishFrame();
 
   void Shutdown();
 
   mojo::gfx::composition::Compositor* compositor_;
   mojo::ui::ViewManager* view_manager_;
 
   mojo::ContextProviderPtr context_provider_;
   mojo::ViewportMetricsPtr viewport_metrics_;
   base::Closure shutdown_callback_;
 
   mojo::Binding<mojo::gfx::composition::SceneListener> scene_listener_binding_;
   mojo::Binding<mojo::ui::ViewTree> view_tree_binding_;
 
   mojo::gfx::composition::ScenePtr scene_;
   mojo::gfx::composition::SceneTokenPtr scene_token_;
   uint32_t scene_version_ = 1u;
 
   mojo::gfx::composition::RendererPtr renderer_;
   mojo::ui::ViewTreeHostPtr view_tree_host_;
   mojo::ui::InputDispatcherPtr input_dispatcher_;
 
-  mojo::ui::ViewTokenPtr root_;
   uint32_t root_key_ = 0u;
+  bool root_was_set_ = false;
   mojo::ui::ViewLayoutInfoPtr root_layout_info_;
 
   DISALLOW_COPY_AND_ASSIGN(LauncherViewTree);
 };
 
 }  // namespace launcher
 
 #endif  // SERVICES_UI_LAUNCHER_VIEW_TREE_IMPL_H_