Refactor SkyShell to allow multiple SkyViews

sky/shell/android/platform_view_android.h

Index: sky/shell/android/platform_view_android.h
diff --git a/sky/shell/android/platform_view_android.h b/sky/shell/android/platform_view_android.h
index 72c8bba079a76cc04a642537a3a1b5b16466f0bc..dce4ee9a2300b41b3cbbe909e00b4625838db65b 100644
--- a/sky/shell/android/platform_view_android.h
+++ b/sky/shell/android/platform_view_android.h
@@ -11,10 +11,13 @@ struct ANativeWindow;
 
 namespace sky {
 namespace shell {
+class Instance;
 
 class PlatformViewAndroid : public PlatformView {
  public:
   static bool Register(JNIEnv* env);
+
+  PlatformViewAndroid(const Config& config);
   ~PlatformViewAndroid() override;
 
   // Called from Java
@@ -22,9 +25,17 @@ class PlatformViewAndroid : public PlatformView {
   void SurfaceCreated(JNIEnv* env, jobject obj, jobject jsurface);
   void SurfaceDestroyed(JNIEnv* env, jobject obj);
 
+  void SetInstance(scoped_ptr<Instance> instance);
+
  private:
   void ReleaseWindow();
 
+  // In principle, the Instance should own the PlatformView, but because our
+  // lifetime is controlled by the Android view hierarchy, we flip around the
+  // ownership and have the Instance owned by Java. We reset this pointer in
+  // |Detach|, which will eventually cause |~PlatformViewAndroid|.
+  scoped_ptr<Instance> instance_;
+
   DISALLOW_COPY_AND_ASSIGN(PlatformViewAndroid);
 };