hide discardable factory from public imagegenerator api

src/lazy/SkDiscardablePixelRef.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 "SkDiscardablePixelRef.h"
 #include "SkDiscardableMemory.h"
 #include "SkImageGenerator.h"
@@ skipping 59 matching lines @@
     rec->fPixels = pixels;
     rec->fColorTable = NULL;
     rec->fRowBytes = fRowBytes;
     return true;
 }
 
 void SkDiscardablePixelRef::onUnlockPixels() {
     fDiscardableMemory->unlock();
 }
 
-bool SkInstallDiscardablePixelRef(SkImageGenerator* generator,
-                                  SkBitmap* dst,
+bool SkInstallDiscardablePixelRef(SkImageGenerator* generator, SkBitmap* dst,
                                   SkDiscardableMemory::Factory* factory) {
     SkImageInfo info;
     SkAutoTDelete<SkImageGenerator> autoGenerator(generator);
     if ((NULL == autoGenerator.get())
         || (!autoGenerator->getInfo(&info))
         || (!dst->setConfig(info, 0))) {
         return false;
     }
     SkASSERT(dst->colorType() != kUnknown_SkColorType);
     if (dst->empty()) {  // Use a normal pixelref.
         return dst->allocPixels();
     }
     SkAutoTUnref<SkDiscardablePixelRef> ref(
         SkNEW_ARGS(SkDiscardablePixelRef,
                    (info, autoGenerator.detach(), dst->rowBytes(), factory)));
     dst->setPixelRef(ref);
     return true;
 }
+
+// This is the public API
+bool SkInstallDiscardablePixelRef(SkImageGenerator* generator, SkBitmap* dst) {
+    return SkInstallDiscardablePixelRef(generator, dst, NULL);
+}
+