Implement Harmony semantics for typeof null (behind a flag).

src/heap.h

 // Copyright 2011 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 142 matching lines @@
   V(constructor_symbol, "constructor")                                   \
   V(code_symbol, ".code")                                                \
   V(result_symbol, ".result")                                            \
   V(catch_var_symbol, ".catch-var")                                      \
   V(empty_symbol, "")                                                    \
   V(eval_symbol, "eval")                                                 \
   V(function_symbol, "function")                                         \
   V(length_symbol, "length")                                             \
   V(name_symbol, "name")                                                 \
   V(native_symbol, "native")                                             \
+  V(null_symbol, "null")                                                 \
   V(number_symbol, "number")                                             \
   V(Number_symbol, "Number")                                             \
   V(nan_symbol, "NaN")                                                   \
   V(RegExp_symbol, "RegExp")                                             \
   V(source_symbol, "source")                                             \
   V(global_symbol, "global")                                             \
   V(ignore_case_symbol, "ignoreCase")                                    \
   V(multiline_symbol, "multiline")                                       \
   V(input_symbol, "input")                                               \
   V(index_symbol, "index")                                               \
@@ skipping 2133 matching lines @@
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG || LIVE_OBJECT_LIST
 
 
 } }  // namespace v8::internal
 
 #undef HEAP
 
 #endif  // V8_HEAP_H_