Added dictionary that can use objects as keys.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 9765fe2a0ab242f897145ea7d763ea21a8616b27..a7b591c6d493e891de29cd1b0984236e2832c12c 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -1640,6 +1640,11 @@ class JSObject: public JSReceiver {
   MUST_USE_RESULT inline MaybeObject* SetHiddenPropertiesObject(
       Object* hidden_obj);
 
+  MUST_USE_RESULT MaybeObject* GetHiddenProperties(bool create_if_needed);
+
+  // Retrieves a permanent object identity hash code.
+  MUST_USE_RESULT MaybeObject* GetIdentityHash();
+
   MUST_USE_RESULT MaybeObject* DeleteProperty(String* name, DeleteMode mode);
   MUST_USE_RESULT MaybeObject* DeleteElement(uint32_t index, DeleteMode mode);
 
@@ -2921,6 +2926,29 @@ class NumberDictionary: public Dictionary<NumberDictionaryShape, uint32_t> {
 };
 
 
+class ObjectDictionaryShape {
+ public:
+  static inline bool IsMatch(JSObject* key, Object* other);
+  static inline uint32_t Hash(JSObject* key);
+  static inline uint32_t HashForObject(JSObject* key, Object* object);
+  MUST_USE_RESULT static inline MaybeObject* AsObject(JSObject* key);
+  static const int kPrefixSize = 2;
+  static const int kEntrySize = 3;
+  static const bool kIsEnumerable = false;
+};
+
+
+class ObjectDictionary: public Dictionary<ObjectDictionaryShape, JSObject*> {
+ public:
+  static inline ObjectDictionary* cast(Object* obj) {
+    ASSERT(obj->IsDictionary());
+    return reinterpret_cast<ObjectDictionary*>(obj);
+  }
+
+  MUST_USE_RESULT MaybeObject* AddChecked(JSObject* key, Object* value);
+};
+
+
 // JSFunctionResultCache caches results of some JSFunction invocation.
 // It is a fixed array with fixed structure:
 //   [0]: factory function