Use safe bool conversion operators in fpdf_page/

core/fpdfapi/fpdf_page/cpdf_colorstate.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.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #ifndef CORE_FPDFAPI_FPDF_PAGE_CPDF_COLORSTATE_H_
 #define CORE_FPDFAPI_FPDF_PAGE_CPDF_COLORSTATE_H_
 
 #include "core/fpdfapi/fpdf_page/cpdf_colorstatedata.h"
@@ skipping 33 matching lines @@
   void SetFillPattern(CPDF_Pattern* pattern,
                       FX_FLOAT* pValue,
                       uint32_t nValues);
   void SetStrokePattern(CPDF_Pattern* pattern,
                         FX_FLOAT* pValue,
                         uint32_t nValues);
 
   // TODO(tsepez): Stop leaking ColorStateData outside this class.
   const CPDF_ColorStateData* GetObject() const { return m_Ref.GetObject(); }
 
-  operator bool() const { return !!m_Ref; }
+  explicit operator bool() const { return !!m_Ref; }
 
  private:
   void SetColor(CPDF_Color& color,
                 uint32_t& rgb,
                 CPDF_ColorSpace* pCS,
                 FX_FLOAT* pValue,
                 uint32_t nValues);
 
   CFX_CountRef<CPDF_ColorStateData> m_Ref;
 };
 
 #endif  // CORE_FPDFAPI_FPDF_PAGE_CPDF_COLORSTATE_H_