[string] Store the correct map during bootstrapping

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/ieee754.h"
 #include "src/code-stubs.h"
@@ skipping 3814 matching lines @@
       Map::CopyInitialMap(handle(object_function->initial_map(), isolate()));
   slow_object_with_null_prototype_map->set_dictionary_map(true);
   Map::SetPrototype(slow_object_with_null_prototype_map,
                     isolate()->factory()->null_value());
   native_context()->set_slow_object_with_null_prototype_map(
       *slow_object_with_null_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());
+  JSObject* string_function_prototype =
+      JSObject::cast(string_function->initial_map()->prototype());
+  DCHECK(string_function_prototype->HasFastProperties());
   native_context()->set_string_function_prototype_map(
-      HeapObject::cast(string_function->map()->prototype())->map());
+      string_function_prototype->map());
 
   Handle<JSGlobalObject> global_object =
       handle(native_context()->global_object());
 
   // Install Global.decodeURI.
   SimpleInstallFunction(global_object, "decodeURI", Builtins::kGlobalDecodeURI,
                         1, false, kGlobalDecodeURI);
 
   // Install Global.decodeURIComponent.
   SimpleInstallFunction(global_object, "decodeURIComponent",
@@ skipping 1026 matching lines @@
 }
 
 
 // Called when the top-level V8 mutex is destroyed.
 void Bootstrapper::FreeThreadResources() {
   DCHECK(!IsActive());
 }
 
 }  // namespace internal
 }  // namespace v8