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

src/builtins.cc

 // 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 177 matching lines @@
   } else {
     // Allocate the JS Array
     JSFunction* constructor =
         Top::context()->global_context()->array_function();
     Object* obj = Heap::AllocateJSObject(constructor);
     if (obj->IsFailure()) return obj;
     array = JSArray::cast(obj);
   }
 
   // 'array' now contains the JSArray we should initialize.
+  ASSERT(array->HasFastElements());
 
   // Optimize the case where there is one argument and the argument is a
   // small smi.
   if (args.length() == 2) {
     Object* obj = args[1];
     if (obj->IsSmi()) {
       int len = Smi::cast(obj)->value();
       if (len >= 0 && len < JSObject::kInitialMaxFastElementArray) {
         Object* obj = Heap::AllocateFixedArrayWithHoles(len);
         if (obj->IsFailure()) return obj;
@@ skipping 1306 matching lines @@
       if (entry->contains(pc)) {
         return names_[i];
       }
     }
   }
   return NULL;
 }
 
 
 } }  // namespace v8::internal