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

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index f1ec56ce5a862ad7a6ae811f1391408335db802c..3098569e3a42313e6d128ae6164c4595b5dad6e6 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -1217,7 +1217,7 @@ Object* Heap::AllocateMap(InstanceType instance_type, int instance_size) {
   map->set_code_cache(empty_fixed_array());
   map->set_unused_property_fields(0);
   map->set_bit_field(0);
-  map->set_bit_field2(1 << Map::kIsExtensible);
+  map->set_bit_field2((1 << Map::kIsExtensible) | (1 << Map::kHasFastElements));
 
   // If the map object is aligned fill the padding area with Smi 0 objects.
   if (Map::kPadStart < Map::kSize) {
@@ -2545,6 +2545,7 @@ Object* Heap::AllocateInitialMap(JSFunction* fun) {
   map->set_inobject_properties(in_object_properties);
   map->set_unused_property_fields(in_object_properties);
   map->set_prototype(prototype);
+  ASSERT(map->has_fast_elements());
 
   // If the function has only simple this property assignments add
   // field descriptors for these to the initial map as the object
@@ -2598,8 +2599,8 @@ Object* Heap::AllocateJSObjectFromMap(Map* map, PretenureFlag pretenure) {
   // properly initialized.
   ASSERT(map->instance_type() != JS_FUNCTION_TYPE);
 
-  // Both types of globla objects should be allocated using
-  // AllocateGloblaObject to be properly initialized.
+  // Both types of global objects should be allocated using
+  // AllocateGlobalObject to be properly initialized.
   ASSERT(map->instance_type() != JS_GLOBAL_OBJECT_TYPE);
   ASSERT(map->instance_type() != JS_BUILTINS_OBJECT_TYPE);
 
@@ -2623,6 +2624,7 @@ Object* Heap::AllocateJSObjectFromMap(Map* map, PretenureFlag pretenure) {
   InitializeJSObjectFromMap(JSObject::cast(obj),
                             FixedArray::cast(properties),
                             map);
+  ASSERT(JSObject::cast(obj)->HasFastElements());
   return obj;
 }