Refactor SkyShell to allow multiple SkyViews

sky/shell/ios/sky_view_controller.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_view_controller.h"
 #import "sky_surface.h"
 
 #import <UIKit/UIKit.h>
 #import <QuartzCore/QuartzCore.h>
 
 @implementation SkyViewController
 
 - (void)loadView {
-  SkySurface* surface = [[SkySurface alloc] init];
+
+  Instance* instance = new sky::shell::Instance(sky::shell::Shell::Shared());
+  SkySurface* surface = [[SkySurface alloc] initWithSkyInstance: instance];
 
   surface.autoresizingMask =
       UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
 
   self.view = surface;
 
   [surface release];
 }
 
 @end