Revert "Enable Object.observe by default"

src/runtime.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 1619 matching lines @@
   }
   return current;
 }
 
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_SetPrototype) {
   HandleScope scope(isolate);
   ASSERT(args.length() == 2);
   CONVERT_ARG_HANDLE_CHECKED(JSObject, obj, 0);
   CONVERT_ARG_HANDLE_CHECKED(Object, prototype, 1);
-  if (obj->map()->is_observed()) {
+  if (FLAG_harmony_observation && obj->map()->is_observed()) {
     Handle<Object> old_value(
         GetPrototypeSkipHiddenPrototypes(isolate, *obj), isolate);
 
     Handle<Object> result = JSObject::SetPrototype(obj, prototype, true);
     RETURN_IF_EMPTY_HANDLE(isolate, result);
 
     Handle<Object> new_value(
         GetPrototypeSkipHiddenPrototypes(isolate, *obj), isolate);
     if (!new_value->SameValue(*old_value)) {
       JSObject::EnqueueChangeRecord(obj, "setPrototype",
@@ skipping 13319 matching lines @@
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags,
                                        "Runtime::PerformGC");
   }
 }
 
 
 } }  // namespace v8::internal