Restore interpretation of Dart null as undefined in dartToScriptValueWithNullCheck.

Source/bindings/dart/DartUtilities.h

Index: Source/bindings/dart/DartUtilities.h
diff --git a/Source/bindings/dart/DartUtilities.h b/Source/bindings/dart/DartUtilities.h
index 132c06686a97a2b5f28934a5efb6792975976305..48afec3d42cce39741d3f521c03bf77b9025b15a 100644
--- a/Source/bindings/dart/DartUtilities.h
+++ b/Source/bindings/dart/DartUtilities.h
@@ -534,6 +534,10 @@ public:
     // to observe from user code.
     static ScriptValue dartToScriptValueWithNullCheck(Dart_Handle handle)
     {
+        if (Dart_IsNull(handle)) {
+            V8ScriptState* scriptState = v8ScriptStateForCurrentIsolate();
+            return ScriptValue(scriptState, v8::Undefined(scriptState->isolate()));

[vsm, 2014/07/01 17:12:52]

Did you consider a DartScriptValue wrapping undefined?  

[rmacnak, 2014/07/01 17:20:02]

Right now a DartScriptValue never has an empty handle, so I considered
interpreting the empty handle as undefined. But this would require special cases
in DartScriptValue toString, toJSON, etc, so I think keeping undefined in V8
land is cleaner.

+        }
         return dartToScriptValue(handle);
     }
     static ScriptValue dartToScriptValueWithNullCheck(Dart_NativeArguments args, int index)