[builtins] Re-add similar String wrapper optimization for StringAdd.

src/contexts.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_CONTEXTS_H_
 #define V8_CONTEXTS_H_
 
 #include "src/heap/heap.h"
 #include "src/objects.h"
 
@@ skipping 201 matching lines @@
   V(JS_SET_FUN_INDEX, JSFunction, js_set_fun)                                  \
   V(JS_SET_MAP_INDEX, Map, js_set_map)                                         \
   V(MAP_CACHE_INDEX, Object, map_cache)                                        \
   V(MAP_ITERATOR_MAP_INDEX, Map, map_iterator_map)                             \
   V(STRING_ITERATOR_MAP_INDEX, Map, string_iterator_map)                       \
   V(MESSAGE_LISTENERS_INDEX, JSObject, message_listeners)                      \
   V(NATIVES_UTILS_OBJECT_INDEX, Object, natives_utils_object)                  \
   V(NORMALIZED_MAP_CACHE_INDEX, Object, normalized_map_cache)                  \
   V(NUMBER_FUNCTION_INDEX, JSFunction, number_function)                        \
   V(OBJECT_FUNCTION_INDEX, JSFunction, object_function)                        \
+  V(OBJECT_FUNCTION_PROTOTYPE_MAP_INDEX, Map, object_function_prototype_map)   \
   V(OPAQUE_REFERENCE_FUNCTION_INDEX, JSFunction, opaque_reference_function)    \
   V(REGEXP_FUNCTION_INDEX, JSFunction, regexp_function)                        \
   V(REGEXP_RESULT_MAP_INDEX, Map, regexp_result_map)                           \
   V(RUNTIME_CONTEXT_INDEX, Context, runtime_context)                           \
   V(SCRIPT_CONTEXT_TABLE_INDEX, ScriptContextTable, script_context_table)      \
   V(SCRIPT_FUNCTION_INDEX, JSFunction, script_function)                        \
   V(SECURITY_TOKEN_INDEX, Object, security_token)                              \
   V(SET_ITERATOR_MAP_INDEX, Map, set_iterator_map)                             \
   V(SHARED_ARRAY_BUFFER_FUN_INDEX, JSFunction, shared_array_buffer_fun)        \
   V(SLOPPY_ARGUMENTS_MAP_INDEX, Map, sloppy_arguments_map)                     \
@@ skipping 319 matching lines @@
   static bool IsBootstrappingOrGlobalObject(Isolate* isolate, Object* object);
 #endif
 
   STATIC_ASSERT(kHeaderSize == Internals::kContextHeaderSize);
   STATIC_ASSERT(EMBEDDER_DATA_INDEX == Internals::kContextEmbedderDataIndex);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_CONTEXTS_H_