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

gm/deviceproperties.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 "SkTypeface.h"
 
 namespace skiagm {
@@ skipping 20 matching lines @@
                              SkScalar degrees,
                              SkScalar px, SkScalar py) {
         canvas->translate(px, py);
         canvas->rotate(degrees);
         canvas->translate(-px, -py);
     }
 
     virtual void onDraw(SkCanvas* originalCanvas) {
         SkISize size = this->getISize();
         SkBitmap bitmap;
-        bitmap.setConfig(SkBitmap::kARGB_8888_Config, size.width(), size.height());
-        bitmap.allocPixels();
+        bitmap.allocN32Pixels(size.width(), size.height());
         SkDeviceProperties properties = SkDeviceProperties::Make(
             SkDeviceProperties::Geometry::Make(SkDeviceProperties::Geometry::kVertical_Orientation,
                                                SkDeviceProperties::Geometry::kBGR_Layout),
             SK_Scalar1);
         SkBitmapDevice device(bitmap, properties);
         SkCanvas canvas(&device);
         canvas.drawColor(SK_ColorWHITE);
 
         SkPaint paint;
 
@@ skipping 51 matching lines @@
 private:
     typedef GM INHERITED;
 };
 
 //////////////////////////////////////////////////////////////////////////////
 
 static GM* MyFactory(void*) { return new DevicePropertiesGM; }
 static GMRegistry reg(MyFactory);
 
 }