add ImageGenerator::NewFromData to porting layer

gm/etc1bitmap.cpp

Index: gm/etc1bitmap.cpp
diff --git a/gm/etc1bitmap.cpp b/gm/etc1bitmap.cpp
index fcf521a1803fec084c3a9ee68eba507bccee2f8b..76593f44414de7c84e9e4edc194dedd6a94423a7 100644
--- a/gm/etc1bitmap.cpp
+++ b/gm/etc1bitmap.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"
 
@@ -103,9 +103,7 @@ protected:
             return;
         }
 
-        if (!SkInstallDiscardablePixelRef(
-                SkDecodingImageGenerator::Create(
-                    fileData, SkDecodingImageGenerator::Options()), &bm)) {
+        if (!SkInstallDiscardablePixelRef(fileData, &bm)) {
             SkDebugf("Could not install discardable pixel ref.\n");
             return;
         }
@@ -204,9 +202,7 @@ protected:
         size_t dataSz = etc1_get_encoded_data_size(width, height) + ETC_PKM_HEADER_SIZE;
         SkAutoDataUnref nonPOTData(SkData::NewWithCopy(am.get(), dataSz));
 
-        if (!SkInstallDiscardablePixelRef(
-                SkDecodingImageGenerator::Create(
-                    nonPOTData, SkDecodingImageGenerator::Options()), &bm)) {
+        if (!SkInstallDiscardablePixelRef(nonPOTData, &bm)) {
             SkDebugf("Could not install discardable pixel ref.\n");
             return;
         }