Add missing operator<() to CFX_RetainPtr

core/fxcrt/cfx_retain_ptr.h

 // Copyright 2016 PDFium 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 CORE_FXCRT_CFX_RETAIN_PTR_H_
 #define CORE_FXCRT_CFX_RETAIN_PTR_H_
 
+#include <functional>
 #include <memory>
 #include <utility>
 
 #include "core/fxcrt/fx_memory.h"
 
+// Analogous to base's scoped_refptr.
 template <class T>
 class CFX_RetainPtr {
  public:
   explicit CFX_RetainPtr(T* pObj) : m_pObj(pObj) {
     if (m_pObj)
       m_pObj->Retain();
   }
 
   CFX_RetainPtr() {}
   CFX_RetainPtr(const CFX_RetainPtr& that) : CFX_RetainPtr(that.Get()) {}
@@ skipping 20 matching lines @@
 
   CFX_RetainPtr& operator=(const CFX_RetainPtr& that) {
     if (*this != that)
       Reset(that.Get());
     return *this;
   }
 
   bool operator==(const CFX_RetainPtr& that) const {
     return Get() == that.Get();
   }
+  bool operator!=(const CFX_RetainPtr& that) const { return !(*this == that); }
 
-  bool operator!=(const CFX_RetainPtr& that) const { return !(*this == that); }
+  bool operator<(const CFX_RetainPtr& that) const {
+    return std::less<T*>()(Get(), that.Get());
+  }
 
   explicit operator bool() const { return !!m_pObj; }
   T& operator*() const { return *m_pObj.get(); }
   T* operator->() const { return m_pObj.get(); }
 
  private:
   std::unique_ptr<T, ReleaseDeleter<T>> m_pObj;
 };
 
 // Trivial implementation - internal ref count with virtual destructor.
@@ skipping 27 matching lines @@
 // Classes managed by CFX_RetainPtr should have protected (or private)
 // constructors, and should friend this function.
 template <typename T, typename... Args>
 CFX_RetainPtr<T> MakeRetain(Args&&... args) {
   return CFX_RetainPtr<T>(new T(std::forward<Args>(args)...));
 }
 
 }  // namespace pdfium
 
 #endif  // CORE_FXCRT_CFX_RETAIN_PTR_H_