[dartium] Use ScriptWrappable when there are multiple Dart wrappers.

Source/bindings/dart/custom/DartWindowCustom.cpp

Index: Source/bindings/dart/custom/DartWindowCustom.cpp
diff --git a/Source/bindings/dart/custom/DartWindowCustom.cpp b/Source/bindings/dart/custom/DartWindowCustom.cpp
index d962408be3bdcb3b3857232291ec01fc0f8acd59..5f8811f1d8e3a1e0eb93661b53717ba30e9c91d1 100644
--- a/Source/bindings/dart/custom/DartWindowCustom.cpp
+++ b/Source/bindings/dart/custom/DartWindowCustom.cpp
@@ -75,6 +75,12 @@ void historyCrossFrameGetter(Dart_NativeArguments args)
         DOMWindow* receiver = DartDOMWrapper::receiver<DOMWindow>(args);
         DartDOMData* domData = static_cast<DartDOMData*>(Dart_GetNativeIsolateData(args));
 
+        Dart_WeakPersistentHandle existingWrapper = DartDOMWrapper::lookupWrapper<DartHistory>(domData, &receiver->history());
+        if (existingWrapper) {
+            Dart_SetWeakHandleReturnValue(args, existingWrapper);
+            return;
+        }
+
         Dart_Handle result = DartDOMWrapper::createWrapper<DartHistory>(
             domData, &receiver->history(), _HistoryCrossFrameClassId);
         if (result)
@@ -88,6 +94,12 @@ void locationCrossFrameGetter(Dart_NativeArguments args)
         DOMWindow* receiver = DartDOMWrapper::receiver<DOMWindow>(args);
         DartDOMData* domData = static_cast<DartDOMData*>(Dart_GetNativeIsolateData(args));
 
+        Dart_WeakPersistentHandle existingWrapper = DartDOMWrapper::lookupWrapper<DartLocation>(domData, &receiver->location());
+        if (existingWrapper) {
+            Dart_SetWeakHandleReturnValue(args, existingWrapper);
+            return;
+        }
+
         Dart_Handle result = DartDOMWrapper::createWrapper<DartLocation>(
             domData, &receiver->location(), _LocationCrossFrameClassId);
         if (result)