Update NulCanvas so everything builds.

experimental/PdfViewer/SkTrackDevice.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkTrackDevice_DEFINED
 #define SkTrackDevice_DEFINED
 
@@ skipping 88 matching lines @@
     void drawSprite(const SkDraw& dummy1, const SkBitmap& bitmap,
                     int x, int y, const SkPaint& paint) override {
         before();
         INHERITED::drawSprite(dummy1, bitmap, x, y, paint);
         after();
     }
 
     void drawBitmapRect(const SkDraw& dummy1, const SkBitmap& dummy2,
                         const SkRect* srcOrNull, const SkRect& dst,
                         const SkPaint& paint,
-                        SK_VIRTUAL_CONSTRAINT_TYPE flags) override {
+                        SkCanvas::SrcRectConstraint flags) override {
         before();
         INHERITED::drawBitmapRect(dummy1, dummy2, srcOrNull, dst, paint, flags);
         after();
     }
 
     void drawText(const SkDraw& dummy1, const void* text, size_t len,
                   SkScalar x, SkScalar y, const SkPaint& paint) override {
         before();
         INHERITED::drawText(dummy1, text, len, x, y, paint);
         after();
@@ skipping 47 matching lines @@
         }
     }
 
 private:
     SkTracker* fTracker;
 
     typedef SkBitmapDevice INHERITED;
 };
 
 #endif  // SkTrackDevice_DEFINED