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

src/bootstrapper.cc

 // Copyright 2014 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.
 
 #include "src/bootstrapper.h"
 
 #include "src/accessors.h"
 #include "src/api-natives.h"
 #include "src/base/utils/random-number-generator.h"
 #include "src/code-stubs.h"
@@ skipping 2316 matching lines @@
     if (!Bootstrapper::CompileBuiltin(isolate(), builtin_index++)) return false;
   }
 
   if (!CallUtilsFunction(isolate(), "PostNatives")) return false;
 
   auto function_cache =
       ObjectHashTable::New(isolate(), ApiNatives::kInitialFunctionCacheSize,
                            USE_CUSTOM_MINIMUM_CAPACITY);
   native_context()->set_function_cache(*function_cache);
 
-  // Store the map for the string prototype after the natives has been compiled
+  // Store the map for the %ObjectPrototype% after the natives has been compiled
+  // and the Object function has been set up.
+  Handle<JSFunction> object_function(native_context()->object_function());
+  DCHECK(JSObject::cast(object_function->initial_map()->prototype())
+             ->HasFastProperties());
+  native_context()->set_object_function_prototype_map(
+      HeapObject::cast(object_function->initial_map()->prototype())->map());
+
+  // Store the map for the %StringPrototype% after the natives has been compiled
   // and the String function has been set up.
   Handle<JSFunction> string_function(native_context()->string_function());
   DCHECK(JSObject::cast(
       string_function->initial_map()->prototype())->HasFastProperties());
   native_context()->set_string_function_prototype_map(
       HeapObject::cast(string_function->initial_map()->prototype())->map());
 
   // Install Date.prototype[@@toPrimitive].
   {
     Handle<String> key = factory()->Date_string();
@@ skipping 910 matching lines @@
 }
 
 
 // Called when the top-level V8 mutex is destroyed.
 void Bootstrapper::FreeThreadResources() {
   DCHECK(!IsActive());
 }
 
 }  // namespace internal
 }  // namespace v8