hide discardable factory from public imagegenerator api

BUG=skia:
R=halcanary@google.com, scroggo@google.com, djsollen@google.com

Author: reed@google.com

Review URL: https://codereview.chromium.org/295243006

git-svn-id: http://skia.googlecode.com/svn/trunk@14889 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tests/CachedDecodingPixelRefTest.cpp b/tests/CachedDecodingPixelRefTest.cpp
index 705f066..10e33ba 100644
--- a/tests/CachedDecodingPixelRefTest.cpp
+++ b/tests/CachedDecodingPixelRefTest.cpp
@@ -12,6 +12,7 @@
 #include "SkDecodingImageGenerator.h"
 #include "SkDiscardableMemoryPool.h"
 #include "SkImageDecoder.h"
+#include "SkImageGeneratorPriv.h"
 #include "SkScaledImageCache.h"
 #include "SkStream.h"
 #include "SkUtils.h"
@@ -152,7 +153,7 @@
     // Use system-default discardable memory.
     return SkInstallDiscardablePixelRef(
         SkDecodingImageGenerator::Create(
-            encoded, SkDecodingImageGenerator::Options()), dst, NULL);
+            encoded, SkDecodingImageGenerator::Options()), dst);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -276,7 +277,7 @@
     SkBitmap bm;
     SkImageGenerator* ig = new TestImageGenerator(
         TestImageGenerator::kSucceedGetPixels_TestType, reporter);
-    SkInstallDiscardablePixelRef(ig, &bm, NULL);
+    SkInstallDiscardablePixelRef(ig, &bm);
     bm.pixelRef()->lockPixels();
 }