Track global cells as special side effects in GVN.

src/unique.h

 // 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 124 matching lines @@
 
   static Unique<T> CreateImmovable(Handle<T> handle) {
     return Unique<T>(reinterpret_cast<Address>(*handle), handle);
   }
 
   friend class UniqueSet<T>;  // Uses internal details for speed.
   template <class U>
   friend class Unique;  // For comparing raw_address values.
 
  private:
+  Unique<T>() : raw_address_(NULL) { }
+
   Address raw_address_;
   Handle<T> handle_;
+
+  friend class SideEffectsTracker;
 };
 
 
 template <typename T>
 class UniqueSet V8_FINAL : public ZoneObject {
  public:
   // Constructor. A new set will be empty.
   UniqueSet() : size_(0), capacity_(0), array_(NULL) { }
 
   // Add a new element to this unique set. Mutates this set. O(|this|).
@@ skipping 166 matching lines @@
       capacity_ = new_capacity;
       array_ = new_array;
     }
   }
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_UNIQUE_H_