Make it possible to run Sky apps offline

sky/engine/core/script/dom_dart_state.h

Index: sky/engine/core/script/dom_dart_state.h
diff --git a/sky/engine/core/script/dom_dart_state.h b/sky/engine/core/script/dom_dart_state.h
index 17088290a699a645c4fe11126722a2e23f0dddc8..ba45f36bafd88ba09cb110a232cfc2499e2da294 100644
--- a/sky/engine/core/script/dom_dart_state.h
+++ b/sky/engine/core/script/dom_dart_state.h
@@ -16,7 +16,7 @@ class LocalDOMWindow;
 
 class DOMDartState : public DartState {
  public:
-  explicit DOMDartState(Document* document, const KURL& url);
+  explicit DOMDartState(Document* document, const String& url);
   ~DOMDartState() override;
 
   virtual void DidSetIsolate();
@@ -27,7 +27,7 @@ class DOMDartState : public DartState {
   static LocalFrame* CurrentFrame();
   static LocalDOMWindow* CurrentWindow();
 
-  const KURL& url() const { return url_; }
+  const String& url() const { return url_; }
 
   Document* document() const { return document_.get(); }
 
@@ -39,7 +39,7 @@ class DOMDartState : public DartState {
 
  private:
   RefPtr<Document> document_;
-  KURL url_;
+  String url_;
 
   DartPersistentValue x_handle_;
   DartPersistentValue y_handle_;