Factor code to rotate a canvas about a point.

gm/imagefilterstransformed.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "sk_tool_utils.h"
 #include "SkBlurImageFilter.h"
 #include "SkColor.h"
@@ skipping 122 matching lines @@
     for (auto& filter : filters) {
         paint.setAntiAlias(false);
         paint.setImageFilter(filter);
 
         canvas->save();
 
         canvas->drawRect(r, paint);
 
         canvas->translate(150, 0);
         canvas->save();
-            canvas->translate(100, 100);
-            canvas->rotate(30);
-            canvas->translate(-100, -100);
+            canvas->rotate(30, 100, 100);
             canvas->drawRect(r, paint);
         canvas->restore();
 
         paint.setAntiAlias(true);
         canvas->translate(150, 0);
         canvas->save();
-            canvas->translate(100, 100);
-            canvas->rotate(30);
-            canvas->translate(-100, -100);
+            canvas->rotate(30, 100, 100);
             canvas->drawRect(r, paint);
         canvas->restore();
 
         canvas->restore();
         canvas->translate(0, 150);
     }
 }