add ImageGenerator::NewFromData to porting layer

BUG=skia:3275

Review URL: https://codereview.chromium.org/834633006
diff --git a/gm/image.cpp b/gm/image.cpp
index 05a3fab..bd7bbe7 100644
--- a/gm/image.cpp
+++ b/gm/image.cpp
@@ -8,7 +8,6 @@
 #include "gm.h"
 #include "SkSurface.h"
 #include "SkCanvas.h"
-#include "SkDecodingImageGenerator.h"
 #include "SkStream.h"
 #include "SkData.h"
 
@@ -24,8 +23,7 @@
     if (NULL == data.get()) {
         return;
     }
-    SkImage* image = SkImage::NewFromGenerator(
-                SkDecodingImageGenerator::Create(data, SkDecodingImageGenerator::Options()));
+    SkImage* image = SkImage::NewFromData(data);
     if (image) {
         SkAutoCanvasRestore acr(canvas, true);
         canvas->scale(size.width() * 1.0f / image->width(),