Make CFX_Color constructor explicit

xfa/fxgraphics/cfx_color.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 XFA_FXGRAPHICS_CFX_COLOR_H_
 #define XFA_FXGRAPHICS_CFX_COLOR_H_
 
 #include "core/fxge/include/fx_dib.h"
 #include "xfa/fxgraphics/include/cfx_graphics.h"
 
 class CFX_Pattern;
 class CFX_Shading;
 
 enum { FX_COLOR_None = 0, FX_COLOR_Solid, FX_COLOR_Pattern, FX_COLOR_Shading };
 
 class CFX_Color {
  public:
   CFX_Color();
-  // TODO(weili): Remove implicit conversions. Make this explicit.
-  CFX_Color(const FX_ARGB argb);
-
-  explicit CFX_Color(CFX_Pattern* pattern, const FX_ARGB argb = 0x0);
+  explicit CFX_Color(const FX_ARGB argb);
   explicit CFX_Color(CFX_Shading* shading);
+  CFX_Color(CFX_Pattern* pattern, const FX_ARGB argb);
   virtual ~CFX_Color();
 
   FWL_Error Set(const FX_ARGB argb);
-  FWL_Error Set(CFX_Pattern* pattern, const FX_ARGB argb = 0x0);
+  FWL_Error Set(CFX_Pattern* pattern, const FX_ARGB argb);
   FWL_Error Set(CFX_Shading* shading);
 
  private:
   friend class CFX_Graphics;
 
   int32_t m_type;
   union {
     struct {
       FX_ARGB argb;
       CFX_Pattern* pattern;
     } m_info;
     CFX_Shading* m_shading;
   };
 };
 
 #endif  // XFA_FXGRAPHICS_CFX_COLOR_H_