some utils for rect and matrix

src/core/SkRRect.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkRRect.h"
 #include "SkMatrix.h"
 
@@ skipping 435 matching lines @@
     }
 
     SkDEBUGCODE(dst->validate();)
 
     return true;
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 
 void SkRRect::inset(SkScalar dx, SkScalar dy, SkRRect* dst) const {
-    SkRect r = fRect;
+    const SkRect r = fRect.makeInset(dx, dy);
 
-    r.inset(dx, dy);
     if (r.isEmpty()) {
         dst->setEmpty();
         return;
     }
 
     SkVector radii[4];
     memcpy(radii, fRadii, sizeof(radii));
     for (int i = 0; i < 4; ++i) {
         if (radii[i].fX) {
             radii[i].fX -= dx;
@@ skipping 121 matching lines @@
     }
 
     for (int i = 0; i < 4; ++i) {
         validate_radius_check_predicates(fRadii[i].fX, fRect.fLeft, fRect.fRight);
         validate_radius_check_predicates(fRadii[i].fY, fRect.fTop, fRect.fBottom);
     }
 }
 #endif // SK_DEBUG
 
 ///////////////////////////////////////////////////////////////////////////////