add ImageGenerator::NewFromData to porting layer

BUG=skia:3275

Review URL: https://codereview.chromium.org/834633006
diff --git a/tests/CachedDecodingPixelRefTest.cpp b/tests/CachedDecodingPixelRefTest.cpp
index b3eb532..48100e7 100644
--- a/tests/CachedDecodingPixelRefTest.cpp
+++ b/tests/CachedDecodingPixelRefTest.cpp
@@ -9,7 +9,6 @@
 #include "SkCachingPixelRef.h"
 #include "SkCanvas.h"
 #include "SkData.h"
-#include "SkDecodingImageGenerator.h"
 #include "SkDiscardableMemoryPool.h"
 #include "SkImageDecoder.h"
 #include "SkImageGeneratorPriv.h"
@@ -143,15 +142,11 @@
 
 ////////////////////////////////////////////////////////////////////////////////
 static bool install_skCachingPixelRef(SkData* encoded, SkBitmap* dst) {
-    return SkCachingPixelRef::Install(
-        SkDecodingImageGenerator::Create(
-            encoded, SkDecodingImageGenerator::Options()), dst);
+    return SkCachingPixelRef::Install(SkImageGenerator::NewFromData(encoded), dst);
 }
 static bool install_skDiscardablePixelRef(SkData* encoded, SkBitmap* dst) {
     // Use system-default discardable memory.
-    return SkInstallDiscardablePixelRef(
-        SkDecodingImageGenerator::Create(
-            encoded, SkDecodingImageGenerator::Options()), dst);
+    return SkInstallDiscardablePixelRef(encoded, dst);
 }
 
 ////////////////////////////////////////////////////////////////////////////////