Fix iOS builds after ShellView refactor on Android

BUG=
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1188633002.

shell/BUILD.gn

@@ -157,6 +157,8 @@ if (is_android) {
         "platform_view.h",
         "shell.cc",
         "shell.h",
+        "shell_view.cc",
+        "shell_view.h",
         "ui/animator.cc",
         "ui/animator.h",
         "ui/engine.cc",

shell/ios/platform_view_ios.h

@@ -12,6 +12,8 @@ namespace shell {
 
 class PlatformViewIOS : public PlatformView {
  public:
+  explicit PlatformViewIOS(const Config& config);
+  ~PlatformViewIOS() override;
   void SurfaceCreated(gfx::AcceleratedWidget widget);
   void SurfaceDestroyed(void);
 

shell/ios/platform_view_ios.mm

@@ -11,6 +11,13 @@ PlatformView* PlatformView::Create(const Config& config) {
   return new PlatformViewIOS(config);
 }
 
+PlatformViewIOS::PlatformViewIOS(const Config& config)
+  : PlatformView(config) {
+}
+
+PlatformViewIOS::~PlatformViewIOS() {
+}
+
 void PlatformViewIOS::SurfaceCreated(gfx::AcceleratedWidget widget) {
   DCHECK(window_ == 0);
   window_ = widget;

shell/ios/sky_surface.h

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #import <UIKit/UIKit.h>
+#import "sky/shell/shell_view.h"
 
 @interface SkySurface : UIView
 

shell/ios/sky_surface.mm

@@ -103,9 +103,8 @@ static inline sky::EventType EventTypeFromUITouchPhase(UITouchPhase phase) {
 }
 
 - (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);

shell/ios/sky_view_controller.mm

@@ -8,13 +8,13 @@
 #import <UIKit/UIKit.h>
 #import <QuartzCore/QuartzCore.h>
 
+#include "sky/shell/shell.h"
 #include "sky/shell/shell_view.h"
 
 @implementation SkyViewController
 
 - (void)loadView {
-
-  ShellView* shell_view = new sky::shell::ShellView(sky::shell::Shell::Shared());
+  auto shell_view = new sky::shell::ShellView(sky::shell::Shell::Shared());
   SkySurface* surface = [[SkySurface alloc] initWithShellView: shell_view];
 
   surface.autoresizingMask =