Make unsafe Unique<T> constructor private.

src/unique.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_HYDROGEN_UNIQUE_H_
 #define V8_HYDROGEN_UNIQUE_H_
 
 #include <ostream>  // NOLINT(readability/streams)
 
 #include "src/base/functional.h"
@@ skipping 14 matching lines @@
 // ability of checking for equality and hashing without accessing the heap.
 //
 // Creating a Unique<T> requires first dereferencing the handle to obtain
 // the address of the object, which is used as the hashcode and the basis for
 // comparison. The object can be moved later by the GC, but comparison
 // and hashing use the old address of the object, without dereferencing it.
 //
 // Careful! Comparison of two Uniques is only correct if both were created
 // in the same "era" of GC or if at least one is a non-movable object.
 template <typename T>
-class Unique {
+class Unique final {
  public:
   Unique<T>() : raw_address_(NULL) {}
 
   // TODO(titzer): make private and introduce a uniqueness scope.
   explicit Unique(Handle<T> handle) {
     if (handle.is_null()) {
       raw_address_ = NULL;
     } else {
       // This is a best-effort check to prevent comparing Unique<T>'s created
       // in different GC eras; we require heap allocation to be disallowed at
       // creation time.
       // NOTE: we currently consider maps to be non-movable, so no special
       // assurance is required for creating a Unique<Map>.
       // TODO(titzer): other immortable immovable objects are also fine.
       DCHECK(!AllowHeapAllocation::IsAllowed() || handle->IsMap());
       raw_address_ = reinterpret_cast<Address>(*handle);
       DCHECK_NOT_NULL(raw_address_);  // Non-null should imply non-zero address.
     }
     handle_ = handle;
   }
 
-  // TODO(titzer): this is a hack to migrate to Unique<T> incrementally.
-  Unique(Address raw_address, Handle<T> handle)
-    : raw_address_(raw_address), handle_(handle) { }
-
   // Constructor for handling automatic up casting.
   // Eg. Unique<JSFunction> can be passed when Unique<Object> is expected.
   template <class S> Unique(Unique<S> uniq) {
 #ifdef DEBUG
     T* a = NULL;
     S* b = NULL;
     a = b;  // Fake assignment to enforce type checks.
     USE(a);
 #endif
     raw_address_ = uniq.raw_address_;
@@ skipping 51 matching lines @@
 
   // TODO(titzer): this is a hack to migrate to Unique<T> incrementally.
   static Unique<T> CreateUninitialized(Handle<T> handle) {
     return Unique<T>(NULL, handle);
   }
 
   static Unique<T> CreateImmovable(Handle<T> handle) {
     return Unique<T>(reinterpret_cast<Address>(*handle), handle);
   }
 
+ private:
+  Unique(Address raw_address, Handle<T> handle)
+      : raw_address_(raw_address), handle_(handle) {}
+
+  Address raw_address_;
+  Handle<T> handle_;
+
   friend class UniqueSet<T>;  // Uses internal details for speed.
   template <class U>
   friend class Unique;  // For comparing raw_address values.
-
- protected:
-  Address raw_address_;
-  Handle<T> handle_;
-
-  friend class SideEffectsTracker;
 };
 
 template <typename T>
 inline std::ostream& operator<<(std::ostream& os, Unique<T> uniq) {
   return os << Brief(*uniq.handle());
 }
 
 
 template <typename T>
 class UniqueSet final : public ZoneObject {
@@ skipping 204 matching lines @@
       }
       capacity_ = new_capacity;
       array_ = new_array;
     }
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_UNIQUE_H_