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

Source/bindings/dart/custom/DartCanvasRenderingContext2DCustom.cpp

 // Copyright 2011, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //    * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //    * Redistributions in binary form must reproduce the above
@@ skipping 53 matching lines @@
         return;
     }
 
     DartUtilities::setDartStringReturnValue(args, style->color());
 }
 
 static PassRefPtr<CanvasStyle> toCanvasStyle(Dart_Handle value)
 {
     Dart_Handle exception = 0;
     DartDOMData* domData = DartDOMData::current();
-    if (DartDOMWrapper::instanceOf<DartCanvasGradient>(domData, value))
+    if (DartDOMWrapper::subtypeOf<DartCanvasGradient>(domData, value))
         return CanvasStyle::createFromGradient(DartCanvasGradient::toNative(value, exception));
 
-    if (DartDOMWrapper::instanceOf<DartCanvasPattern>(domData, value))
+    if (DartDOMWrapper::subtypeOf<DartCanvasPattern>(domData, value))
         return CanvasStyle::createFromPattern(DartCanvasPattern::toNative(value, exception));
 
     return 0;
 }
 
 void strokeStyleGetter(Dart_NativeArguments args )
 {
     {
         CanvasRenderingContext2D* receiver = DartDOMWrapper::receiver<CanvasRenderingContext2D>(args);
 
@@ skipping 58 matching lines @@
     }
 
 fail:
     Dart_ThrowException(exception);
     ASSERT_NOT_REACHED();
 }
 
 } // namespace DartCanvasRenderingContext2DInternal
 
 } // namespace WebCore