Revert of Change SkDecodingImageGenerator API

src/lazy/SkCachingPixelRef.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 "SkCachingPixelRef.h"
 #include "SkScaledImageCache.h"
 
 
 bool SkCachingPixelRef::Install(SkImageGenerator* generator,
                                 SkBitmap* dst) {
     SkImageInfo info;
+    SkASSERT(generator != NULL);
     SkASSERT(dst != NULL);
     if ((NULL == generator)
         || !(generator->getInfo(&info))
         || !dst->setConfig(info, 0)) {
         SkDELETE(generator);
         return false;
     }
     SkAutoTUnref<SkCachingPixelRef> ref(SkNEW_ARGS(SkCachingPixelRef,
                                            (info, generator, dst->rowBytes())));
     dst->setPixelRef(ref);
@@ skipping 60 matching lines @@
     // reference to the concrete PixelRef while this record is
     // locked.
     return pixels;
 }
 
 void SkCachingPixelRef::onUnlockPixels() {
     SkASSERT(fScaledCacheId != NULL);
     SkScaledImageCache::Unlock( static_cast<SkScaledImageCache::ID*>(fScaledCacheId));
     fScaledCacheId = NULL;
 }