Guard against undefined fields in global context.

src/assembler.h

 // Copyright (c) 1994-2006 Sun Microsystems 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.
 //
@@ skipping 572 matching lines @@
   static ExternalReference perform_gc_function(Isolate* isolate);
   static ExternalReference fill_heap_number_with_random_function(
       Isolate* isolate);
   static ExternalReference random_uint32_function(Isolate* isolate);
   static ExternalReference transcendental_cache_array_address(Isolate* isolate);
   static ExternalReference delete_handle_scope_extensions(Isolate* isolate);
 
   // Deoptimization support.
   static ExternalReference new_deoptimizer_function(Isolate* isolate);
   static ExternalReference compute_output_frames_function(Isolate* isolate);
-  static ExternalReference global_contexts_list(Isolate* isolate);
 
   // Static data in the keyed lookup cache.
   static ExternalReference keyed_lookup_cache_keys(Isolate* isolate);
   static ExternalReference keyed_lookup_cache_field_offsets(Isolate* isolate);
 
   // Static variable Heap::roots_array_start()
   static ExternalReference roots_array_start(Isolate* isolate);
 
   // Static variable StackGuard::address_of_jslimit()
   static ExternalReference address_of_stack_limit(Isolate* isolate);
@@ skipping 271 matching lines @@
  public:
   NullCallWrapper() { }
   virtual ~NullCallWrapper() { }
   virtual void BeforeCall(int call_size) const { }
   virtual void AfterCall() const { }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_ASSEMBLER_H_