Revert "Enable Object.observe by default"

src/accessors.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 582 matching lines @@
   Handle<Object> value(value_raw, isolate);
   if (!function->should_have_prototype()) {
     // Since we hit this accessor, object will have no prototype property.
     Handle<Object> result = JSObject::SetLocalPropertyIgnoreAttributes(object,
         isolate->factory()->prototype_string(), value, NONE);
     RETURN_IF_EMPTY_HANDLE(isolate, result);
     return *result;
   }
 
   Handle<Object> old_value;
-  bool is_observed = *function == *object && function->map()->is_observed();
+  bool is_observed =
+      FLAG_harmony_observation &&
+      *function == *object &&
+      function->map()->is_observed();
   if (is_observed) {
     if (function->has_prototype())
       old_value = handle(function->prototype(), isolate);
     else
       old_value = isolate->factory()->NewFunctionPrototype(function);
   }
 
   JSFunction::SetPrototype(function, value);
   ASSERT(function->prototype() == *value);
 
@@ skipping 351 matching lines @@
   info->set_data(Smi::FromInt(index));
   Handle<Object> getter = v8::FromCData(isolate, &ModuleGetExport);
   Handle<Object> setter = v8::FromCData(isolate, &ModuleSetExport);
   info->set_getter(*getter);
   if (!(attributes & ReadOnly)) info->set_setter(*setter);
   return info;
 }
 
 
 } }  // namespace v8::internal