Object.observe: prevent observed objects from using fast elements.

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 13366 matching lines @@
     if (obj->IsNull()) return isolate->heap()->undefined_value();
     ASSERT(proto->IsJSGlobalObject());
     obj = JSReceiver::cast(proto);
   }
   if (obj->map()->is_observed() != is_observed) {
     MaybeObject* maybe = obj->map()->Copy();
     Map* map;
     if (!maybe->To(&map)) return maybe;
     map->set_is_observed(is_observed);
     obj->set_map(map);
+    if (is_observed && obj->IsJSObject() &&
+        !JSObject::cast(obj)->HasExternalArrayElements()) {
+      // Go to dictionary mode, so that we don't skip map checks.
+      maybe = JSObject::cast(obj)->NormalizeElements();
+      if (maybe->IsFailure()) return maybe;
+      ASSERT(!JSObject::cast(obj)->HasFastElements());
+    }
   }
   return isolate->heap()->undefined_value();
 }
 
 
 RUNTIME_FUNCTION(MaybeObject*, Runtime_SetObserverDeliveryPending) {
   ASSERT(args.length() == 0);
   isolate->set_observer_delivery_pending(true);
   return isolate->heap()->undefined_value();
 }
@@ skipping 118 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