Every place where AllocationMemento is initialized with an

src/hydrogen.cc

 // Copyright 2013 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 1813 matching lines @@
 HValue* HGraphBuilder::BuildCreateAllocationMemento(HValue* previous_object,
                                                     int previous_object_size,
                                                     HValue* alloc_site) {
   // TODO(mvstanton): ASSERT altered to CHECK to diagnose chromium bug 284577
   CHECK(alloc_site != NULL);
   HInnerAllocatedObject* alloc_memento = Add<HInnerAllocatedObject>(
       previous_object, previous_object_size);
   Handle<Map> alloc_memento_map(
       isolate()->heap()->allocation_memento_map());
   AddStoreMapConstant(alloc_memento, alloc_memento_map);
+
+  // TODO(mvstanton): the code below is turned on to diagnose chromium bug
+  // 284577.
+  Handle<Map> alloc_site_map(isolate()->heap()->allocation_site_map());
+  IfBuilder builder(this);
+  // Read the map
+  HValue* map_field = Add<HLoadNamedField>(alloc_site,
+                                           HObjectAccess::ForMap());
+  HValue* alloc_site_map_value = Add<HConstant>(alloc_site_map);
+  builder.IfNot<HCompareObjectEqAndBranch>(map_field, alloc_site_map_value);
+  builder.Then();
+  AddInstruction(new(zone()) HDebugBreak());
+  builder.End();
+
   HObjectAccess access = HObjectAccess::ForAllocationMementoSite();
   Add<HStoreNamedField>(alloc_memento, access, alloc_site);
   return alloc_memento;
 }
 
 
 HInstruction* HGraphBuilder::BuildGetNativeContext() {
   // Get the global context, then the native context
   HInstruction* global_object = Add<HGlobalObject>();
   HObjectAccess access = HObjectAccess::ForJSObjectOffset(
@@ skipping 7836 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal