Fix iOS builds after ShellView refactor on Android

sky/shell/ios/sky_surface.mm

 // 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.
 
 #import "sky_surface.h"
 
 #import <QuartzCore/QuartzCore.h>
 #import <OpenGLES/EAGL.h>
 #import <OpenGLES/EAGLDrawable.h>
 
@@ skipping 85 matching lines @@
 
 - (void)notifySurfaceCreation {
   self.platformView->SurfaceCreated(self.acceleratedWidget);
 }
 
 - (NSString*)skyInitialLoadURL {
   return [NSBundle mainBundle].infoDictionary[@"com.google.sky.load_url"];
 }
 
 - (void)connectToViewportObserverAndLoad {
-  auto view = static_cast<sky::shell::PlatformViewIOS*>(_shell_view->view());
   auto interface_request = mojo::GetProxy(&_viewport_observer);
-  view->ConnectToViewportObserver(interface_request.Pass());
+  self.platformView->ConnectToViewportObserver(interface_request.Pass());
 
   mojo::String string(self.skyInitialLoadURL.UTF8String);
   _viewport_observer->LoadURL(string);
 }
 
 - (void)notifySurfaceDestruction {
   self.platformView->SurfaceDestroyed();
 }
 
 #pragma mark - UIResponder overrides for raw touches
@@ skipping 42 matching lines @@
 + (Class)layerClass {
   return [CAEAGLLayer class];
 }
 
 - (void)dealloc {
   [self notifySurfaceDestruction];
   [super dealloc];
 }
 
 @end