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

gm/offsetimagefilter.cpp

 /*
  * Copyright 2013 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 "SkOffsetImageFilter.h"
 #include "SkBitmapSource.h"
 
 #define WIDTH 400
 #define HEIGHT 100
 #define MARGIN 12
 
 namespace skiagm {
 
 class OffsetImageFilterGM : public GM {
 public:
     OffsetImageFilterGM() : fInitialized(false) {
         this->setBGColor(0xFF000000);
     }
 
 protected:
     virtual SkString onShortName() {
         return SkString("offsetimagefilter");
     }
 
     void make_bitmap() {
-        fBitmap.setConfig(SkBitmap::kARGB_8888_Config, 80, 80);
-        fBitmap.allocPixels();
+        fBitmap.allocN32Pixels(80, 80);
         SkBitmapDevice device(fBitmap);
         SkCanvas canvas(&device);
         canvas.clear(0x00000000);
         SkPaint paint;
         paint.setAntiAlias(true);
         paint.setColor(0xD000D000);
         paint.setTextSize(SkIntToScalar(96));
         const char* str = "e";
         canvas.drawText(str, strlen(str), SkIntToScalar(15), SkIntToScalar(65), paint);
     }
@@ skipping 71 matching lines @@
     SkBitmap fBitmap, fCheckerboard;
     bool fInitialized;
 };
 
 //////////////////////////////////////////////////////////////////////////////
 
 static GM* MyFactory(void*) { return new OffsetImageFilterGM; }
 static GMRegistry reg(MyFactory);
 
 }