Change mapRectScaleTranslate to pass args/ret by value

bench/MatrixBench.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 "Benchmark.h"
 #include "SkMatrix.h"
 #include "SkMatrixUtils.h"
 #include "SkRandom.h"
@@ skipping 302 matching lines @@
         fM.setScale(2, 3);
         fM.postTranslate(1, 2);
 
         fR.set(10, 10, 100, 200);
     }
 
     void performTest() override {
         SkRect dst;
         if (fScaleTrans) {
             for (int i = 0; i < MEGA_LOOP; ++i) {
-                fM.mapRectScaleTranslate(&dst, fR);
+                dst = fM.mapRectScaleTranslate(fR);
             }
         } else {
             for (int i = 0; i < MEGA_LOOP; ++i) {
                 fM.mapRect(&dst, fR);
             }
         }
     }
 };
 DEF_BENCH( return new MapRectMatrixBench("maprect", false); )
 DEF_BENCH( return new MapRectMatrixBench("maprectscaletrans", true); )