Revert "Enable Object.observe by default"

src/ic.cc

 // Copyright 2012 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 1185 matching lines @@
   // Check if the given name is an array index.
   uint32_t index;
   if (name->AsArrayIndex(&index)) {
     Handle<Object> result =
         JSObject::SetElement(receiver, index, value, NONE, strict_mode());
     RETURN_IF_EMPTY_HANDLE(isolate(), result);
     return *value;
   }
 
   // Observed objects are always modified through the runtime.
-  if (receiver->map()->is_observed()) {
+  if (FLAG_harmony_observation && receiver->map()->is_observed()) {
     Handle<Object> result = JSReceiver::SetProperty(
         receiver, name, value, NONE, strict_mode(), store_mode);
     RETURN_IF_EMPTY_HANDLE(isolate(), result);
     return *result;
   }
 
   // Use specialized code for setting the length of arrays with fast
   // properties. Slow properties might indicate redefinition of the length
   // property. Note that when redefined using Object.freeze, it's possible
   // to have fast properties but a read-only length.
@@ skipping 446 matching lines @@
   Handle<Code> stub = generic_stub();
 
   if (key->IsInternalizedString()) {
     maybe_object = StoreIC::Store(object,
                                   Handle<String>::cast(key),
                                   value,
                                   JSReceiver::MAY_BE_STORE_FROM_KEYED);
     if (maybe_object->IsFailure()) return maybe_object;
   } else {
     bool use_ic = FLAG_use_ic && !object->IsAccessCheckNeeded() &&
-        !(object->IsJSObject() &&
+        !(FLAG_harmony_observation && object->IsJSObject() &&
           JSObject::cast(*object)->map()->is_observed());
     if (use_ic && !object->IsSmi()) {
       // Don't use ICs for maps of the objects in Array's prototype chain. We
       // expect to be able to trap element sets to objects with those maps in
       // the runtime to enable optimization of element hole access.
       Handle<HeapObject> heap_object = Handle<HeapObject>::cast(object);
       if (heap_object->map()->IsMapInArrayPrototypeChain()) use_ic = false;
     }
 
     if (use_ic) {
@@ skipping 1133 matching lines @@
 #undef ADDR
 };
 
 
 Address IC::AddressFromUtilityId(IC::UtilityId id) {
   return IC_utilities[id];
 }
 
 
 } }  // namespace v8::internal