Give generatored bindings classes a field remembering an index into a cache of handles on the corre…

tools/dom/templates/html/dartium/cpp_implementation.template

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // WARNING: Do not edit - generated code.
 
 #include "config.h"
+#include "DartWebkitClassIds.h"
 #include "Dart$(INTERFACE).h"
 
 $INCLUDES
 namespace WebCore {
 
 Dart_Handle $(WEBCORE_CLASS_NAME_ESCAPED)_toDart(PassRefPtr< $WEBCORE_CLASS_NAME > value) {
     return Dart$INTERFACE::toDart(value);
 }
 
 namespace Dart$(INTERFACE)Internal {
 $CALLBACKS
 }
 
 Dart_NativeFunction Dart$(INTERFACE)::resolver(Dart_Handle nameHandle, int argumentCount)
 {
     String name = DartUtilities::toString(nameHandle);
 
 $RESOLVER
     return 0;
 }
 
 const char* const Dart$(INTERFACE)::dartImplementationClassName = "$DART_IMPLEMENTATION_CLASS";
 const char* const Dart$(INTERFACE)::dartImplementationLibraryName = "$DART_IMPLEMENTATION_LIBRARY";
-
+const int Dart$(INTERFACE)::dartClassId = $(INTERFACE)ClassId;
 }