pdfviewer: make pdfviewer compile on mac

experimental/PdfViewer/SkPdfGraphicsState.h

 #ifndef __DEFINED__SkPdfBasics
 #define __DEFINED__SkPdfBasics
 
 #include "SkCanvas.h"
 #include "SkPaint.h"
 #include "SkPdfConfig.h"
 #include "SkPdfUtils.h"
 
 #include <stack>
 
@@ skipping 341 matching lines @@
         fBlendModes[0] = SkXfermode::kSrc_Mode;  // PDF: Normal Blend mode
         fSMask        = NULL;
     }
 
     // TODO(edisonn): make two functons instead, stroking and non stoking, avoid branching
     void applyGraphicsState(SkPaint* paint, bool stroking);
 };
 
 // TODO(edisonn): better class design.
 // TODO(edisonn): rename to SkPdfContext
-struct SkPdfContext {
-    std::stack<SkPdfNativeObject*>        fObjectStack;
+class SkPdfContext {
+public:
+    std::stack<SkPdfNativeObject*>  fObjectStack;
     std::stack<SkPdfGraphicsState>  fStateStack;
     SkPdfGraphicsState              fGraphicsState;
-    SkPdfNativeDoc*              fPdfDoc;
+    SkPdfNativeDoc*                 fPdfDoc;
     // TODO(edisonn): the allocator, could be freed after the page is done drawing.
     SkPdfAllocator*                 fTmpPageAllocator;
     SkMatrix                        fOriginalMatrix;
 
     SkPdfContext(SkPdfNativeDoc* doc);
     ~SkPdfContext();
 };
 
 #endif  // __DEFINED__SkPdfBasics