Refactor SkyShell to allow multiple SkyViews

sky/shell/platform_view.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 SKY_SHELL_PLATFORM_VIEW_H_
 #define SKY_SHELL_PLATFORM_VIEW_H_
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "sky/shell/ui_delegate.h"
 
 namespace sky {
 namespace shell {
 
 class PlatformView {
  public:
   struct Config {
     base::WeakPtr<UIDelegate> ui_delegate;
     scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner;
   };
 
-  explicit PlatformView(const Config& config);
+  static PlatformView* Create(const Config& config);
+
   virtual ~PlatformView();
 
   void ConnectToViewportObserver(
       mojo::InterfaceRequest<ViewportObserver> request);
 
  protected:
+  explicit PlatformView(const Config& config);
+
   void SurfaceWasCreated();
   void SurfaceWasDestroyed();
 
   Config config_;
   gfx::AcceleratedWidget window_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(PlatformView);
 };
 
 }  // namespace shell
 }  // namespace sky
 
 #endif  // SKY_SHELL_PLATFORM_VIEW_H_