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

gm/giantbitmap.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"
 #include "SkCanvas.h"
 #include "SkColorPriv.h"
 #include "SkShader.h"
 
 /*
  *  Want to ensure that our bitmap sampler (in bitmap shader) keeps plenty of
  *  precision when scaling very large images (where the dx might get very small.
  */
 
 #define W   257
 #define H   161
 
 class GiantBitmapGM : public skiagm::GM {
     SkBitmap* fBM;
     SkShader::TileMode fMode;
     bool fDoFilter;
     bool fDoRotate;
 
     const SkBitmap& getBitmap() {
         if (NULL == fBM) {
             fBM = new SkBitmap;
-            fBM->setConfig(SkBitmap::kARGB_8888_Config, W, H);
-            fBM->allocPixels();
+            fBM->allocN32Pixels(W, H);
             fBM->eraseColor(SK_ColorWHITE);
 
             const SkColor colors[] = {
                 SK_ColorBLUE, SK_ColorRED, SK_ColorBLACK, SK_ColorGREEN
             };
 
             SkCanvas canvas(*fBM);
             SkPaint paint;
             paint.setAntiAlias(true);
             paint.setStrokeWidth(SkIntToScalar(20));
@@ skipping 103 matching lines @@
 static skiagm::GMRegistry reg010(G010);
 static skiagm::GMRegistry reg110(G110);
 static skiagm::GMRegistry reg210(G210);
 
 static skiagm::GMRegistry reg001(G001);
 static skiagm::GMRegistry reg101(G101);
 static skiagm::GMRegistry reg201(G201);
 static skiagm::GMRegistry reg011(G011);
 static skiagm::GMRegistry reg111(G111);
 static skiagm::GMRegistry reg211(G211);