pdfviewer: debug code for crash

Review URL: https://codereview.chromium.org/22269002

git-svn-id: http://skia.googlecode.com/svn/trunk@10548 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/experimental/PdfViewer/SkPdfBasics.h b/experimental/PdfViewer/SkPdfBasics.h
index 662e745..7016339 100644
--- a/experimental/PdfViewer/SkPdfBasics.h
+++ b/experimental/PdfViewer/SkPdfBasics.h
@@ -350,6 +350,7 @@
         fDashPhase    = 0;
         fBlendModesLength = 1;
         fBlendModes[0] = SkXfermode::kSrc_Mode;  // PDF: Normal Blend mode
+        fSMask        = NULL;
     }
 
     // TODO(edisonn): make two functons instead, stroking and non stoking, avoid branching