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

src/objects-inl.h

Index: src/objects-inl.h
===================================================================
--- src/objects-inl.h	(revision 556)
+++ src/objects-inl.h	(working copy)
@@ -354,6 +354,11 @@
 }
 
 
+bool Object::IsLookupCache() {
+  return IsHashTable();
+}
+
+
 bool Object::IsPrimitive() {
   return IsOddball() || IsNumber() || IsString();
 }
@@ -1186,6 +1191,7 @@
 CAST_ACCESSOR(SymbolTable)
 CAST_ACCESSOR(CompilationCacheTable)
 CAST_ACCESSOR(MapCache)
+CAST_ACCESSOR(LookupCache)
 CAST_ACCESSOR(String)
 CAST_ACCESSOR(SeqString)
 CAST_ACCESSOR(SeqAsciiString)