explicit operator bool for CFX_RetainPtr and CFX_CountRef

core/fxcrt/include/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_INCLUDE_CFX_RETAIN_PTR_H_
 #define CORE_FXCRT_INCLUDE_CFX_RETAIN_PTR_H_
 
 #include <memory>
 
 #include "core/fxcrt/include/fx_memory.h"
@@ skipping 28 matching lines @@
       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); }
 
-  operator bool() const { return !!m_pObj; }
+  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;
 };
 
 #endif  // CORE_FXCRT_INCLUDE_CFX_RETAIN_PTR_H_