Make code compile with clang_use_chrome_plugin (part I)

core/fpdfapi/fpdf_page/cpdf_shadingpattern.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_SHADINGPATTERN_H_
 #define CORE_FPDFAPI_FPDF_PAGE_CPDF_SHADINGPATTERN_H_
 
 #include <memory>
@@ skipping 22 matching lines @@
 class CPDF_Object;
 
 class CPDF_ShadingPattern : public CPDF_Pattern {
  public:
   CPDF_ShadingPattern(CPDF_Document* pDoc,
                       CPDF_Object* pPatternObj,
                       FX_BOOL bShading,
                       const CFX_Matrix& parentMatrix);
   ~CPDF_ShadingPattern() override;
 
-  CPDF_TilingPattern* AsTilingPattern() override { return nullptr; }
-  CPDF_ShadingPattern* AsShadingPattern() override { return this; }
+  CPDF_TilingPattern* AsTilingPattern() override;
+  CPDF_ShadingPattern* AsShadingPattern() override;
 
   bool IsMeshShading() const {
     return m_ShadingType == kFreeFormGouraudTriangleMeshShading ||
            m_ShadingType == kLatticeFormGouraudTriangleMeshShading ||
            m_ShadingType == kCoonsPatchMeshShading ||
            m_ShadingType == kTensorProductPatchMeshShading;
   }
   bool Load();
 
   ShadingType GetShadingType() const { return m_ShadingType; }
@@ skipping 11 matching lines @@
 
   // Still keep |m_pCS| as some CPDF_ColorSpace (name object) are not managed
   // as counted objects. Refer to CPDF_DocPageData::GetColorSpace.
   CPDF_ColorSpace* m_pCS;
 
   CPDF_CountedColorSpace* m_pCountedCS;
   std::vector<std::unique_ptr<CPDF_Function>> m_pFunctions;
 };
 
 #endif  // CORE_FPDFAPI_FPDF_PAGE_CPDF_SHADINGPATTERN_H_