Reapply "Move isolate loading to a separate loader isolate."

Source/bindings/dart/DartDOMData.h

Index: Source/bindings/dart/DartDOMData.h
diff --git a/Source/bindings/dart/DartDOMData.h b/Source/bindings/dart/DartDOMData.h
index f05266de2ea2ffac485fdebee15f0179dd9f0c10..128252d3a2e5a7b01cdc0ed3008651b1069b23d7 100644
--- a/Source/bindings/dart/DartDOMData.h
+++ b/Source/bindings/dart/DartDOMData.h
@@ -64,6 +64,7 @@ class ActiveDOMObject;
 class CustomElementDefinition;
 class DOMWindow;
 class DartApplicationLoader;
+class DartAsyncLoader;
 class DartEventListener;
 class DartIsolateDestructionObserver;
 class DartWeakCallback;
@@ -104,6 +105,10 @@ public:
 
     void setApplicationLoader(PassRefPtr<DartApplicationLoader>);
     PassRefPtr<DartApplicationLoader> applicationLoader();
+
+    void setAsyncLoader(PassRefPtr<DartAsyncLoader>);
+    PassRefPtr<DartAsyncLoader> asyncLoader();
+
     Vector<uint8_t>* applicationSnapshot() { return &m_applicationSnapshot; }
 
     void setReachableWeakHandle(Dart_WeakPersistentHandle reachableWeakHandle)
@@ -213,6 +218,7 @@ private:
     RefPtr<ThreadSafeDartIsolateWrapper> m_threadSafeIsolateWrapper;
     Mutex m_isolateWrapperMutex;
     RefPtr<DartApplicationLoader> m_applicationLoader;
+    RefPtr<DartAsyncLoader> m_asyncLoader;
     Vector<uint8_t> m_applicationSnapshot;
     Dart_WeakPersistentHandle m_reachableWeakHandle;