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/tools/LazyDecodeBitmap.cpp b/tools/LazyDecodeBitmap.cpp
index 83fca5f..6c4160c 100644
--- a/tools/LazyDecodeBitmap.cpp
+++ b/tools/LazyDecodeBitmap.cpp
@@ -10,7 +10,7 @@
 #include "SkData.h"
 #include "SkDecodingImageGenerator.h"
 #include "SkDiscardableMemoryPool.h"
-#include "SkImageGenerator.h"
+#include "SkImageGeneratorPriv.h"
 #include "SkForceLinking.h"
 
 #include "SkCommandLineFlags.h"