make allocPixels throw on failure

tests/BitmapTest.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 "SkBitmap.h"
 
 #include "Test.h"
@@ skipping 57 matching lines @@
  *  This test contains basic sanity checks concerning bitmaps.
  */
 DEF_TEST(Bitmap, reporter) {
     // Zero-sized bitmaps are allowed
     for (int width = 0; width < 2; ++width) {
         for (int height = 0; height < 2; ++height) {
             SkBitmap bm;
             bool setConf = bm.setInfo(SkImageInfo::MakeN32Premul(width, height));
             REPORTER_ASSERT(reporter, setConf);
             if (setConf) {
-                REPORTER_ASSERT(reporter, bm.allocPixels(NULL));
+                bm.allocPixels();
             }
             REPORTER_ASSERT(reporter, SkToBool(width & height) != bm.empty());
         }
     }
 
     test_bigwidth(reporter);
     test_allocpixels(reporter);
 }