Introduce a PrototypeIterator class and use it for prototype access

src/objects.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_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include "src/allocation.h"
 #include "src/assert-scope.h"
 #include "src/builtins.h"
@@ skipping 1496 matching lines @@
       Isolate* isolate,
       Handle<Object> object,
       uint32_t index);
 
   MUST_USE_RESULT static MaybeHandle<Object> GetElementWithReceiver(
       Isolate* isolate,
       Handle<Object> object,
       Handle<Object> receiver,
       uint32_t index);
 
-  // Return the object's prototype (might be Heap::null_value()).
-  Object* GetPrototype(Isolate* isolate);
-  static Handle<Object> GetPrototype(Isolate* isolate, Handle<Object> object);
-
   // Returns the permanent hash code associated with this object. May return
   // undefined if not yet created.
   Object* GetHash();
 
   // Returns the permanent hash code associated with this object depending on
   // the actual object type. May create and store a hash code if needed and none
   // exists.
   static Handle<Smi> GetOrCreateHash(Isolate* isolate, Handle<Object> object);
 
   // Checks whether this object has the same value as the given one.  This
@@ skipping 36 matching lines @@
 
 #ifdef OBJECT_PRINT
   // For our gdb macros, we should perhaps change these in the future.
   void Print();
 
   // Prints this object with details.
   void Print(OStream& os);  // NOLINT
 #endif
 
  private:
+  friend class PrototypeIterator;
+
+  // Return the map of the root of object's prototype chain.
+  Map* GetRootMap(Isolate* isolate);
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(Object);
 };
 
 
 struct Brief {
   explicit Brief(const Object* const v) : value(v) {}
   const Object* value;
 };
 
 
@@ skipping 9644 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_