hide discardable factory from public imagegenerator api

tests/CachedDecodingPixelRefTest.cpp

Index: tests/CachedDecodingPixelRefTest.cpp
diff --git a/tests/CachedDecodingPixelRefTest.cpp b/tests/CachedDecodingPixelRefTest.cpp
index 705f0666a46c5efb79a4d158b0a76af67e910bc7..10e33ba841be16bbb079ad4397a340a53bd949c2 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 @@ static bool install_skDiscardablePixelRef(SkData* encoded, SkBitmap* dst) {
     // Use system-default discardable memory.
     return SkInstallDiscardablePixelRef(
         SkDecodingImageGenerator::Create(
-            encoded, SkDecodingImageGenerator::Options()), dst, NULL);
+            encoded, SkDecodingImageGenerator::Options()), dst);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -276,7 +277,7 @@ static void test_newlockdelete(skiatest::Reporter* reporter) {
     SkBitmap bm;
     SkImageGenerator* ig = new TestImageGenerator(
         TestImageGenerator::kSucceedGetPixels_TestType, reporter);
-    SkInstallDiscardablePixelRef(ig, &bm, NULL);
+    SkInstallDiscardablePixelRef(ig, &bm);
     bm.pixelRef()->lockPixels();
 }