Refactor SkyShell to allow multiple SkyViews

sky/shell/ios/sky_surface.mm

Index: sky/shell/ios/sky_surface.mm
diff --git a/sky/shell/ios/sky_surface.mm b/sky/shell/ios/sky_surface.mm
index d8056de84be340b5ef24f8ff7d26072376583706..2eea5a89cb747112c48285b37c105c865b45027e 100644
--- a/sky/shell/ios/sky_surface.mm
+++ b/sky/shell/ios/sky_surface.mm
@@ -38,6 +38,14 @@ static inline sky::EventType EventTypeFromUITouchPhase(UITouchPhase phase) {
   BOOL _platformViewInitialized;
 
   sky::ViewportObserverPtr _viewport_observer;
+  scoped_ptr<sky::shell::Instance> _instance;
+}
+
+-(instancetype) initWithSkyInstance:(sky::shell::Instance *) instance {
+  self = [super init];
+  if (self)
+    _instance.reset(instance);
+  return self;
 }
 
 - (gfx::AcceleratedWidget)acceleratedWidget {
@@ -80,8 +88,7 @@ static inline sky::EventType EventTypeFromUITouchPhase(UITouchPhase phase) {
 }
 
 - (sky::shell::PlatformViewIOS*)platformView {
-  auto view = static_cast<sky::shell::PlatformViewIOS*>(
-      sky::shell::Shell::Shared().view());
+  auto view = static_cast<sky::shell::PlatformViewIOS*>(_instance->view());
   DCHECK(view);
   return view;
 }
@@ -95,7 +102,7 @@ static inline sky::EventType EventTypeFromUITouchPhase(UITouchPhase phase) {
 }
 
 - (void)connectToViewportObserverAndLoad {
-  auto view = sky::shell::Shell::Shared().view();
+  auto view = static_cast<sky::shell::PlatformViewIOS*>(_instance->view());
   auto interface_request = mojo::GetProxy(&_viewport_observer);
   view->ConnectToViewportObserver(interface_request.Pass());