Make PlatformViewport and NativeViewportImpl use Shell* instead of ApplicationImpl*.

services/native_viewport/app_delegate.cc

Index: services/native_viewport/app_delegate.cc
diff --git a/services/native_viewport/app_delegate.cc b/services/native_viewport/app_delegate.cc
index f1f53fcc0b3aba7f34b454adbebfccad0d4ac58b..e0aeda1bcc45876bccc91126745340186f0a81ce 100644
--- a/services/native_viewport/app_delegate.cc
+++ b/services/native_viewport/app_delegate.cc
@@ -66,7 +66,7 @@ bool NativeViewportAppDelegate::ConfigureIncomingConnection(
       mojo::InterfaceRequest<mojo::NativeViewport> native_viewport_request) {
     if (!gpu_state_.get())
       gpu_state_ = new gles2::GpuState();
-    new NativeViewportImpl(application_, is_headless_, gpu_state_,
+    new NativeViewportImpl(application_->shell(), is_headless_, gpu_state_,
                            native_viewport_request.Pass());
   });