Fixed minor c++ issues found by cppcheck

http://codereview.appspot.com/6127049/



git-svn-id: http://skia.googlecode.com/svn/trunk@3771 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/pdf/SkPDFShader.h b/src/pdf/SkPDFShader.h
index afa63e7..f41bdf0 100644
--- a/src/pdf/SkPDFShader.h
+++ b/src/pdf/SkPDFShader.h
@@ -60,6 +60,7 @@
     static void RemoveShader(SkPDFObject* shader);
 
     SkPDFShader();
+    virtual ~SkPDFShader() {};
 
     virtual bool isValid() = 0;
 };