Allow native_viewport to create new native windows on demand on Android.

services/native_viewport/native_viewport_impl.h

Index: services/native_viewport/native_viewport_impl.h
diff --git a/services/native_viewport/native_viewport_impl.h b/services/native_viewport/native_viewport_impl.h
index 15de028f5f3119c36ccf106e00e74cd5c8a8aa5a..d21bb7ab4bb9e7bbb54845462027477ad6473d0a 100644
--- a/services/native_viewport/native_viewport_impl.h
+++ b/services/native_viewport/native_viewport_impl.h
@@ -59,6 +59,13 @@ class NativeViewportImpl : public mojo::NativeViewport,
   bool OnEvent(mojo::EventPtr event) override;
   void OnDestroyed() override;
 
+  // Get a weak pointer to this object.
+  base::WeakPtr<NativeViewportImpl> GetWeakPtr();
+  // Notify the associated PlatformViewport that a new native surface is
+  // available. Returns true if the new surface has been attached to, false
+  // otherwise.
+  bool NewNativeSurfaceAvailable();
+
  private:
   // Callback when the dispatcher has processed a message we're waiting on
   // an ack from. |pointer_id| identifies the pointer the message was associated