add legacy/helper allocN32Pixels, and convert gm to use it

gm/ninepatchstretch.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"
 
 static void make_bitmap(SkBitmap* bitmap, SkIRect* center) {
     const int kFixed = 28;
     const int kStretchy = 8;
     const int kSize = 2*kFixed + kStretchy;
 
-    bitmap->setConfig(SkBitmap::kARGB_8888_Config, kSize, kSize);
-    bitmap->allocPixels();
+    bitmap->allocN32Pixels(kSize, kSize);
     SkBaseDevice* dev = new SkBitmapDevice(*bitmap);
 
     SkCanvas canvas(dev);
     dev->unref();
     canvas.clear(SK_ColorTRANSPARENT);
 
     SkRect r = SkRect::MakeWH(SkIntToScalar(kSize), SkIntToScalar(kSize));
     const SkScalar strokeWidth = SkIntToScalar(6);
     const SkScalar radius = SkIntToScalar(kFixed) - strokeWidth/2;
 
@@ skipping 65 matching lines @@
 private:
     typedef GM INHERITED;
 };
 
 //////////////////////////////////////////////////////////////////////////////
 
 static GM* MyFactory(void*) { return new NinePatchStretchGM; }
 static GMRegistry reg(MyFactory);
 
 }