add ImageGenerator::NewFromData to porting layer

gm/astcbitmap.cpp

Index: gm/astcbitmap.cpp
diff --git a/gm/astcbitmap.cpp b/gm/astcbitmap.cpp
index 3c9079cfa80df8e8110520981fedb15073ac1b1d..ea97f0b8e28765ac2d6d76250b6a17a07e654bf2 100644
--- a/gm/astcbitmap.cpp
+++ b/gm/astcbitmap.cpp
@@ -10,7 +10,7 @@
 #include "Resources.h"
 #include "SkCanvas.h"
 #include "SkData.h"
-#include "SkDecodingImageGenerator.h"
+#include "SkImageGenerator.h"
 #include "SkImageDecoder.h"
 #include "SkOSFile.h"
 #include "SkTextureCompressor.h"
@@ -76,9 +76,7 @@ protected:
                 }
 
                 SkBitmap bm;
-                if (!SkInstallDiscardablePixelRef(
-                        SkDecodingImageGenerator::Create(
-                            fileData, SkDecodingImageGenerator::Options()), &bm)) {
+                if (!SkInstallDiscardablePixelRef(SkImageGenerator::NewFromData(fileData), &bm)) {
                     SkDebugf("Could not install discardable pixel ref.\n");
                     return;
                 }