quick fix to land clear() change

BUG=skia:
TBR=
NOTRY=True

Review URL: https://codereview.chromium.org/774863003
diff --git a/experimental/PdfViewer/SkTrackDevice.h b/experimental/PdfViewer/SkTrackDevice.h
index 8d6a923..9280b7f 100644
--- a/experimental/PdfViewer/SkTrackDevice.h
+++ b/experimental/PdfViewer/SkTrackDevice.h
@@ -39,11 +39,13 @@
     }
 
 protected:
+#if 0   // clear is deprecated (and private)
     virtual void clear(SkColor color) {
         before();
         INHERITED::clear(color);
         after();
     }
+#endif
 
     virtual void drawPaint(const SkDraw& dummy1, const SkPaint& paint) {
         before();