hide discardable factory from public imagegenerator api

src/core/SkImageGeneratorPriv.h

+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkImageGeneratorPriv_DEFINED
+#define SkImageGeneratorPriv_DEFINED
+
+#include "SkImageGenerator.h"
+#include "SkDiscardableMemory.h"
+
+/**
+ *  Takes ownership of SkImageGenerator.  If this method fails for
+ *  whatever reason, it will return false and immediatetely delete
+ *  the generator.  If it succeeds, it will modify destination
+ *  bitmap.
+ *
+ *  If generator is NULL, will safely return false.
+ *
+ *  If this fails or when the SkDiscardablePixelRef that is
+ *  installed into destination is destroyed, it will call
+ *  SkDELETE() on the generator.  Therefore, generator should be
+ *  allocated with SkNEW() or SkNEW_ARGS().
+ *
+ *  @param destination Upon success, this bitmap will be
+ *  configured and have a pixelref installed.
+ *
+ *  @param factory If not NULL, this object will be used as a
+ *  source of discardable memory when decoding.  If NULL, then
+ *  SkDiscardableMemory::Create() will be called.
+ *
+ *  @return true iff successful.
+ */
+bool SkInstallDiscardablePixelRef(SkImageGenerator*, SkBitmap* destination,
+                                  SkDiscardableMemory::Factory* factory);
+
+#endif