allow clip calls w/o op param, remove unnecessary kReplace ops

gm/clip_strokerect.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "gm.h"
 #include "SkCanvas.h"
 #include "SkPath.h"
@@ skipping 18 matching lines @@
         p.setColor(SK_ColorRED);
         p.setAntiAlias(true);
         p.setStyle(SkPaint::kStroke_Style);
         p.setStrokeWidth(22);
 
         SkRect r = SkRect::MakeXYWH(20, 20, 100, 100);
         // setting the height of this to 19 causes failure
         SkRect rect = SkRect::MakeXYWH(20, 0, 100, 20);
 
         canvas->save();
-        canvas->clipRect(rect, SkCanvas::kReplace_Op, true);
+        canvas->clipRect(rect, true);
         canvas->drawRect(r, p);
         canvas->restore();
 
         p.setColor(SK_ColorBLUE);
         p.setStrokeWidth(2);
         canvas->drawRect(rect, p);
 
         p.setColor(SK_ColorRED);
         p.setAntiAlias(true);
         p.setStyle(SkPaint::kStroke_Style);
         p.setStrokeWidth(22);
 
         SkRect r2 = SkRect::MakeXYWH(20, 140, 100, 100);
         // setting the height of this to 19 causes failure
         SkRect rect2 = SkRect::MakeXYWH(20, 120, 100, 19);
 
         canvas->save();
-        canvas->clipRect(rect2, SkCanvas::kReplace_Op, true);
+        canvas->clipRect(rect2, true);
         canvas->drawRect(r2, p);
         canvas->restore();
 
         p.setColor(SK_ColorBLUE);
         p.setStrokeWidth(2);
         canvas->drawRect(rect2, p);
     }
 
 private:
     typedef skiagm::GM INHERITED;
 };
 
 DEF_GM(return new ClipStrokeRectGM;)