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

gm/bicubicfilter.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 "SkColor.h"
 #include "SkBicubicImageFilter.h"
 
 namespace skiagm {
 
 class BicubicGM : public GM {
 public:
     BicubicGM() : fInitialized(false) {
         this->setBGColor(0x00000000);
     }
 
 protected:
     virtual SkString onShortName() {
         return SkString("bicubicfilter");
     }
 
     void make_checkerboard(int width, int height) {
         SkASSERT(width % 2 == 0);
         SkASSERT(height % 2 == 0);
-        fCheckerboard.setConfig(SkBitmap::kARGB_8888_Config, width, height);
-        fCheckerboard.allocPixels();
-        SkAutoLockPixels lock(fCheckerboard);
+        fCheckerboard.allocN32Pixels(width, height);
         for (int y = 0; y < height; y += 2) {
             SkPMColor* s = fCheckerboard.getAddr32(0, y);
             for (int x = 0; x < width; x += 2) {
                 *s++ = 0xFFFFFFFF;
                 *s++ = 0xFF000000;
             }
             s = fCheckerboard.getAddr32(0, y + 1);
             for (int x = 0; x < width; x += 2) {
                 *s++ = 0xFF000000;
                 *s++ = 0xFFFFFFFF;
@@ skipping 34 matching lines @@
     SkBitmap fCheckerboard;
     bool fInitialized;
 };
 
 //////////////////////////////////////////////////////////////////////////////
 
 static GM* MyFactory(void*) { return new BicubicGM; }
 static GMRegistry reg(MyFactory);
 
 }