Revert r14023 (Unify code for fast and slow path of JSON.stringify) from trunk.

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index b3be86b7feb5be68c74101de5edb0640242a9923..90f2e60e9b88ffbf90f1672a0a4b71471d302080 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -220,7 +220,6 @@ namespace internal {
   V(undefined_string, "undefined")                                       \
   V(value_of_string, "valueOf")                                          \
   V(stack_string, "stack")                                               \
-  V(toJSON_string, "toJSON")                                             \
   V(InitializeVarGlobal_string, "InitializeVarGlobal")                   \
   V(InitializeConstGlobal_string, "InitializeConstGlobal")               \
   V(KeyedLoadElementMonomorphic_string,                                  \