Introduce a lookup cache class in the runtime system and use it for...

src/heap.h

Index: src/heap.h
===================================================================
--- src/heap.h	(revision 556)
+++ src/heap.h	(working copy)
@@ -122,7 +122,8 @@
   V(Code, c_entry_debug_break_code)                     \
   V(FixedArray, number_string_cache)                    \
   V(FixedArray, single_character_string_cache)          \
-  V(FixedArray, natives_source_cache)
+  V(FixedArray, natives_source_cache)                   \
+  V(Object, keyed_lookup_cache)
 
 
 #define ROOT_LIST(V)                                  \
@@ -639,6 +640,11 @@
     non_monomorphic_cache_ = value;
   }
 
+  // Gets, sets and clears the lookup cache used for keyed access.
+  static inline Object* GetKeyedLookupCache();
+  static inline void SetKeyedLookupCache(LookupCache* cache);
+  static inline void ClearKeyedLookupCache();
+
 #ifdef DEBUG
   static void Print();
   static void PrintHandles();