add ImageGenerator::NewFromData to porting layer

src/lazy/SkDiscardablePixelRef.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkDiscardablePixelRef.h"
 #include "SkDiscardableMemory.h"
 #include "SkImageGenerator.h"
@@ skipping 98 matching lines @@
     if (dst->empty()) {  // Use a normal pixelref.
         return dst->tryAllocPixels();
     }
     SkAutoTUnref<SkDiscardablePixelRef> ref(
         SkNEW_ARGS(SkDiscardablePixelRef,
                    (info, autoGenerator.detach(), dst->rowBytes(), factory)));
     dst->setPixelRef(ref);
     return true;
 }
 
-// This is the public API
+// These are the public API
+
 bool SkInstallDiscardablePixelRef(SkImageGenerator* generator, SkBitmap* dst) {
     return SkInstallDiscardablePixelRef(generator, dst, NULL);
 }
+
+bool SkInstallDiscardablePixelRef(SkData* encoded, SkBitmap* dst) {
+    SkImageGenerator* generator = SkImageGenerator::NewFromData(encoded);
+    return generator ? SkInstallDiscardablePixelRef(generator, dst, NULL) : false;
+}