Make code compile with clang_use_chrome_plugin (part I)

This change contains files in core/fpdfapi directory. This is part
of the efforts to make PDFium code compilable by Clang chromium
style plugins.

The changes are mainly the following:
-- move inline constructor/destructor of complex class/struct out-of-line;
-- add constructor/destructor of complex class/struct if not
   explicitly defined;
-- add explicit out-of-line copy constructor when needed;
-- move inline virtual functions out-of-line;
-- Properly mark virtual functions with 'override';
-- some minor cleanups;

BUG=pdfium:469

Review-Url: https://codereview.chromium.org/2060973002

1 files changed, 2 insertions, 2 deletions

diff --git a/core/fpdfapi/fpdf_page/cpdf_shadingpattern.h b/core/fpdfapi/fpdf_page/cpdf_shadingpattern.h
index f5cef17fb1..7fe2cc6c79 100644
--- a/core/fpdfapi/fpdf_page/cpdf_shadingpattern.h
+++ b/core/fpdfapi/fpdf_page/cpdf_shadingpattern.h
@@ -40,8 +40,8 @@ class CPDF_ShadingPattern : public CPDF_Pattern {
                       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 ||