Extract shell methods from ApplicationImpl into a base class, and pass this to Initialize() instead.

components/mus/mus_app.h

Index: components/mus/mus_app.h
diff --git a/components/mus/mus_app.h b/components/mus/mus_app.h
index e30060299a8ceb7209e1777c5ad9470789885c25..920e6688b2194dafa82cf2f26b2b9776dc8b6951 100644
--- a/components/mus/mus_app.h
+++ b/components/mus/mus_app.h
@@ -24,7 +24,7 @@
 #include "mojo/shell/public/cpp/interface_factory.h"
 
 namespace mojo {
-class ApplicationImpl;
+class Shell;
 }
 
 namespace ui {
@@ -61,7 +61,8 @@ class MandolineUIServicesApp
   struct PendingRequest;
 
   // ApplicationDelegate:
-  void Initialize(mojo::ApplicationImpl* app) override;
+  void Initialize(mojo::Shell* shell, const std::string& url,
+                  uint32_t id) override;
   bool AcceptConnection(
       mojo::ApplicationConnection* connection) override;
 
@@ -103,7 +104,7 @@ class MandolineUIServicesApp
                             mojom::WindowTreeClientPtr tree_client) override;
 
   mojo::WeakBindingSet<mojom::WindowTreeHostFactory> factory_bindings_;
-  mojo::ApplicationImpl* app_impl_;
+  mojo::Shell* shell_;
   scoped_ptr<ws::ConnectionManager> connection_manager_;
   scoped_refptr<GpuState> gpu_state_;
   scoped_ptr<ui::PlatformEventSource> event_source_;