hide discardable factory from public imagegenerator api

tests/PictureTest.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmapDevice.h"
 #include "SkBlurImageFilter.h"
 #include "SkCanvas.h"
@@ skipping 1095 matching lines @@
     SkBitmap original;
     make_bm(&original, 100, 100, SK_ColorBLUE, true);
     SkDynamicMemoryWStream wStream;
     if (!SkImageEncoder::EncodeStream(&wStream, original, SkImageEncoder::kPNG_Type, 100)) {
         return;
     }
     SkAutoDataUnref data(wStream.copyToData());
 
     SkBitmap bm;
     bool installSuccess = SkInstallDiscardablePixelRef(
-         SkDecodingImageGenerator::Create(data, SkDecodingImageGenerator::Options()), &bm, NULL);
+         SkDecodingImageGenerator::Create(data, SkDecodingImageGenerator::Options()), &bm);
     REPORTER_ASSERT(reporter, installSuccess);
 
     // Write both bitmaps to pictures, and ensure that the resulting data streams are the same.
     // Flattening original will follow the old path of performing an encode, while flattening bm
     // will use the already encoded data.
     SkAutoDataUnref picture1(serialized_picture_from_bitmap(original));
     SkAutoDataUnref picture2(serialized_picture_from_bitmap(bm));
     REPORTER_ASSERT(reporter, picture1->equals(picture2));
     // Now test that a parse error was generated when trying to create a new SkPicture without
     // providing a function to decode the bitmap.
@@ skipping 373 matching lines @@
     SkAutoTUnref<SkPicture> picture(recorder.endRecording());
 }
 
 DEF_TEST(Canvas_EmptyBitmap, r) {
     SkBitmap dst;
     dst.allocN32Pixels(10, 10);
     SkCanvas canvas(dst);
 
     test_draw_bitmaps(&canvas);
 }