add a default value for return value

src/arguments.h

 // Copyright 2012 the V8 project authors. 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
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 235 matching lines @@
   PropertyCallbackArguments(Isolate* isolate,
                             Object* data,
                             Object* self,
                             JSObject* holder)
       : Super(isolate) {
     Object** values = this->end();
     values[T::kThisIndex] = self;
     values[T::kHolderIndex] = holder;
     values[T::kDataIndex] = data;
     values[T::kIsolateIndex] = reinterpret_cast<Object*>(isolate);
+    values[T::kReturnValueDefaultValueIndex] =

[Sven Panne, 2013/06/10 07:24:00]

How do we make sure that the hole never escapes to JavaScript land? I can't
immediately see why this is guaranteed, so at least a comment might be
appropriate.

+        isolate->heap()->the_hole_value();
     values[T::kReturnValueIndex] = isolate->heap()->the_hole_value();
     ASSERT(values[T::kHolderIndex]->IsHeapObject());
     ASSERT(values[T::kIsolateIndex]->IsSmi());
   }
 
   /*
    * The following Call functions wrap the calling of all callbacks to handle
    * calling either the old or the new style callbacks depending on which one
    * has been registered.
    * For old callbacks which return an empty handle, the ReturnValue is checked
@@ skipping 40 matching lines @@
       bool is_construct_call)
         : Super(isolate),
           argv_(argv),
           argc_(argc),
           is_construct_call_(is_construct_call) {
     Object** values = end();
     values[T::kDataIndex] = data;
     values[T::kCalleeIndex] = callee;
     values[T::kHolderIndex] = holder;
     values[T::kIsolateIndex] = reinterpret_cast<internal::Object*>(isolate);
+    values[T::kReturnValueDefaultValueIndex] =

[Sven Panne, 2013/06/10 07:24:00]

Same here.

+        isolate->heap()->the_hole_value();
     values[T::kReturnValueIndex] = isolate->heap()->the_hole_value();
     ASSERT(values[T::kCalleeIndex]->IsJSFunction());
     ASSERT(values[T::kHolderIndex]->IsHeapObject());
     ASSERT(values[T::kIsolateIndex]->IsSmi());
   }
 
   /*
    * The following Call function wraps the calling of all callbacks to handle
    * calling either the old or the new style callbacks depending on which one
    * has been registered.
@@ skipping 20 matching lines @@
   return __RT_impl_##Name(args, isolate);                             \
 }                                                                     \
 static Type __RT_impl_##Name(Arguments args, Isolate* isolate)
 
 #define RUNTIME_ARGUMENTS(isolate, args) \
   args.length(), args.arguments(), isolate
 
 } }  // namespace v8::internal
 
 #endif  // V8_ARGUMENTS_H_