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

gm/samplerstress.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 "gm.h"
 #include "SkCanvas.h"
 #include "SkShader.h"
@@ skipping 29 matching lines @@
      * Create a red & green stripes on black texture
      */
     void createTexture() {
         if (fTextureCreated) {
             return;
         }
 
         static const int xSize = 16;
         static const int ySize = 16;
 
-        fTexture.setConfig(SkBitmap::kARGB_8888_Config,
-                           xSize,
-                           ySize,
-                           xSize*sizeof(SkColor));
-
-        fTexture.allocPixels();
-        fTexture.lockPixels();
+        fTexture.allocN32Pixels(xSize, ySize);
         SkPMColor* addr = fTexture.getAddr32(0, 0);
 
         for (int y = 0; y < ySize; ++y) {
             for (int x = 0; x < xSize; ++x) {
                 addr[y*xSize+x] = SkPreMultiplyColor(SK_ColorBLACK);
 
                 if ((y % 5) == 0) {
                     addr[y*xSize+x] = SkPreMultiplyColor(SK_ColorRED);
                 }
                 if ((x % 7) == 0) {
                     addr[y*xSize+x] = SkPreMultiplyColor(SK_ColorGREEN);
                 }
             }
         }
 
-        fTexture.unlockPixels();
-
         fTextureCreated = true;
     }
 
     void createShader() {
         if (NULL != fShader.get()) {
             return;
         }
 
         createTexture();
 
@@ skipping 67 matching lines @@
 
     typedef GM INHERITED;
 };
 
 //////////////////////////////////////////////////////////////////////////////
 
 static GM* MyFactory(void*) { return new SamplerStressGM; }
 static GMRegistry reg(MyFactory);
 
 }