Rename ViewportObserver to SkyEngine

sky/shell/platform_view.cc

Index: sky/shell/platform_view.cc
diff --git a/sky/shell/platform_view.cc b/sky/shell/platform_view.cc
index 0a6431dc5ee89205219b962c1b658baa67a4e2d4..a22fc5df808437e5decc2a016bb322141a59a5b2 100644
--- a/sky/shell/platform_view.cc
+++ b/sky/shell/platform_view.cc
@@ -24,10 +24,10 @@ PlatformView::PlatformView(const PlatformView::Config& config)
 PlatformView::~PlatformView() {
 }
 
-void PlatformView::ConnectToViewportObserver(
-    mojo::InterfaceRequest<ViewportObserver> request) {
+void PlatformView::ConnectToEngine(
+    mojo::InterfaceRequest<SkyEngine> request) {
   config_.ui_task_runner->PostTask(
-      FROM_HERE, base::Bind(&UIDelegate::ConnectToViewportObserver,
+      FROM_HERE, base::Bind(&UIDelegate::ConnectToEngine,
                             config_.ui_delegate, base::Passed(&request)));
 }