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

gm/aarectmodes.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"
@@ skipping 90 matching lines @@
     SkRect rect = SkRect::MakeXYWH(W / 4 + offset,
                                    H / 4 + offset,
                                    W / 2, H / 2);
     canvas->drawRect(rect, paint);
 
     return H;
 }
 
 static SkShader* make_bg_shader() {
     SkBitmap bm;
-    bm.setConfig(SkBitmap::kARGB_8888_Config, 2, 2);
-    bm.allocPixels();
+    bm.allocN32Pixels(2, 2);
     *bm.getAddr32(0, 0) = *bm.getAddr32(1, 1) = 0xFFFFFFFF;
     *bm.getAddr32(1, 0) = *bm.getAddr32(0, 1) = SkPackARGB32(0xFF, 0xCC,
                                                              0xCC, 0xCC);
 
     SkShader* s = SkShader::CreateBitmapShader(bm,
                                                SkShader::kRepeat_TileMode,
                                                SkShader::kRepeat_TileMode);
 
     SkMatrix m;
     m.setScale(SkIntToScalar(6), SkIntToScalar(6));
@@ skipping 57 matching lines @@
     private:
         typedef GM INHERITED;
     };
 
 //////////////////////////////////////////////////////////////////////////////
 
     static GM* MyFactory(void*) { return new AARectModesGM; }
     static GMRegistry reg(MyFactory);
 
 }