[turbofan] Add support for extending properties backing store.

src/compiler/js-native-context-specialization.h

 // Copyright 2015 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_COMPILER_JS_NATIVE_CONTEXT_SPECIALIZATION_H_
 #define V8_COMPILER_JS_NATIVE_CONTEXT_SPECIALIZATION_H_
 
 #include "src/base/flags.h"
 #include "src/compiler/graph-reducer.h"
 #include "src/deoptimize-reason.h"
@@ skipping 114 matching lines @@
                                         AccessMode access_mode,
                                         KeyedAccessStoreMode store_mode);
 
   // Construct an appropriate heap object check.
   Node* BuildCheckHeapObject(Node* receiver, Node** effect, Node* control);
 
   // Construct an appropriate map check.
   Node* BuildCheckMaps(Node* receiver, Node* effect, Node* control,
                        std::vector<Handle<Map>> const& maps);
 
+  // Construct appropriate subgraph to extend properties backing store.
+  Node* BuildExtendPropertiesBackingStore(Handle<Map> map, Node* properties,
+                                          Node* effect, Node* control);
+
   // Adds stability dependencies on all prototypes of every class in
   // {receiver_type} up to (and including) the {holder}.
   void AssumePrototypesStable(std::vector<Handle<Map>> const& receiver_maps,
                               Handle<JSObject> holder);
 
   // Checks if we can turn the hole into undefined when loading an element
   // from an object with one of the {receiver_maps}; sets up appropriate
   // code dependencies and might use the array protector cell.
   bool CanTreatHoleAsUndefined(std::vector<Handle<Map>> const& receiver_maps);
 
@@ skipping 51 matching lines @@
   DISALLOW_COPY_AND_ASSIGN(JSNativeContextSpecialization);
 };
 
 DEFINE_OPERATORS_FOR_FLAGS(JSNativeContextSpecialization::Flags)
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_JS_NATIVE_CONTEXT_SPECIALIZATION_H_