Add "has fast elements" bit to maps and use it in inlined keyed loads.

src/factory.h

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 162 matching lines @@
   static Handle<JSObject> NewFunctionPrototype(Handle<JSFunction> function);
 
   static Handle<Map> CopyMapDropDescriptors(Handle<Map> map);
 
   // Copy the map adding more inobject properties if possible without
   // overflowing the instance size.
   static Handle<Map> CopyMap(Handle<Map> map, int extra_inobject_props);
 
   static Handle<Map> CopyMapDropTransitions(Handle<Map> map);
 
+  static Handle<Map> GetFastElementsMap(Handle<Map> map);
+
+  static Handle<Map> GetSlowElementsMap(Handle<Map> map);
+
   static Handle<FixedArray> CopyFixedArray(Handle<FixedArray> array);
 
   // Numbers (eg, literals) are pretenured by the parser.
   static Handle<Object> NewNumber(double value,
                                   PretenureFlag pretenure = NOT_TENURED);
 
   static Handle<Object> NewNumberFromInt(int value);
   static Handle<Object> NewNumberFromUint(uint32_t value);
 
   // These objects are used by the api to create env-independent data
@@ skipping 201 matching lines @@
   // Update the map cache in the global context with (keys, map)
   static Handle<MapCache> AddToMapCache(Handle<Context> context,
                                         Handle<FixedArray> keys,
                                         Handle<Map> map);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_FACTORY_H_