change mapRectScaleTranslate to pass args/ret by value

tests/MatrixTest.cpp

Index: tests/MatrixTest.cpp
diff --git a/tests/MatrixTest.cpp b/tests/MatrixTest.cpp
index c4eb9c7011e35c6f72bdd5fde6b42360fda90155..4386c5f491f1fb7eb06e2d9e0dd45e48f828da0f 100644
--- a/tests/MatrixTest.cpp
+++ b/tests/MatrixTest.cpp
@@ -978,7 +978,7 @@ DEF_TEST(Matrix_maprects, r) {
         mat.mapPoints((SkPoint*)&dst[0].fLeft, (SkPoint*)&src.fLeft, 2);
         dst[0].sort();
         mat.mapRect(&dst[1], src);
-        mat.mapRectScaleTranslate(&dst[2], src);
+        dst[2] = mat.mapRectScaleTranslate(src);
 
         REPORTER_ASSERT(r, dst[0] == dst[1]);
         REPORTER_ASSERT(r, dst[0] == dst[2]);