Use Dart_InstanceIsSubtypeOf to check if instance is a direct subtype of specified type.

Source/bindings/dart/DartUtilities.cpp

Index: Source/bindings/dart/DartUtilities.cpp
===================================================================
--- Source/bindings/dart/DartUtilities.cpp	(revision 1430)
+++ Source/bindings/dart/DartUtilities.cpp	(working copy)
@@ -342,7 +342,7 @@
 bool DartUtilities::isHtmlElement(DartDOMData* domData, Dart_Handle handle)
 {
     ASSERT(domData);
-    return DartDOMWrapper::instanceOf<DartHTMLElement>(domData, handle);
+    return DartDOMWrapper::subtypeOf<DartHTMLElement>(domData, handle);
 }
 
 bool DartUtilities::isDateTime(DartDOMData* domData, Dart_Handle handle)
@@ -357,19 +357,19 @@
 bool DartUtilities::isBlob(DartDOMData* domData, Dart_Handle handle)
 {
     ASSERT(domData);
-    return DartDOMWrapper::instanceOf<DartBlob>(domData, handle);
+    return DartDOMWrapper::subtypeOf<DartBlob>(domData, handle);
 }
 
 bool DartUtilities::isImageData(DartDOMData* domData, Dart_Handle handle)
 {
     ASSERT(domData);
-    return DartDOMWrapper::instanceOf<DartImageData>(domData, handle);
+    return DartDOMWrapper::subtypeOf<DartImageData>(domData, handle);
 }
 
 bool DartUtilities::isIDBKeyRange(DartDOMData* domData, Dart_Handle handle)
 {
     ASSERT(domData);
-    return DartDOMWrapper::instanceOf<DartIDBKeyRange>(domData, handle);
+    return DartDOMWrapper::subtypeOf<DartIDBKeyRange>(domData, handle);
 }
 
 bool DartUtilities::objectIsType(Dart_Handle handle, Dart_Handle type)
@@ -803,7 +803,7 @@
     DartDOMData* domData = DartDOMData::current();
     for (size_t i = 0; i < elements.size(); i++) {
         Dart_Handle element = elements[i];
-        if (DartDOMWrapper::instanceOf<DartMessagePort>(domData, element)) {
+        if (DartDOMWrapper::subtypeOf<DartMessagePort>(domData, element)) {
             MessagePort* messagePort = DartMessagePort::toNative(element, exception);
             ASSERT(!exception);
             ASSERT(messagePort);