Make Failure inherit from MaybeObject instead of Object.

src/globals.h

Index: src/globals.h
===================================================================
--- src/globals.h	(revision 5696)
+++ src/globals.h	(working copy)
@@ -324,6 +324,7 @@
 class NewSpace;
 class NodeVisitor;
 class Object;
+class MaybeObject;
 class OldSpace;
 class Property;
 class Proxy;
@@ -542,8 +543,8 @@
 
 // AccessorCallback
 struct AccessorDescriptor {
-  Object* (*getter)(Object* object, void* data);
-  Object* (*setter)(JSObject* object, Object* value, void* data);
+  MaybeObject* (*getter)(Object* object, void* data);
+  MaybeObject* (*setter)(JSObject* object, Object* value, void* data);
   void* data;
 };