change pixel-serializer to support reencoding existing data

tests/ImageTest.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCanvas.h"
 #include "SkData.h"
 #include "SkDevice.h"
@@ skipping 101 matching lines @@
 
 const char* kSerializedData = "serialized";
 
 class MockSerializer : public SkPixelSerializer {
 public:
     MockSerializer(SkData* (*func)()) : fFunc(func), fDidEncode(false) { }
 
     bool didEncode() const { return fDidEncode; }
 
 protected:
-    bool onUseEncodedData(const void*, size_t) override {
-        return false;
+    SkData* onReencodeData(SkData*) override {
+        return nullptr;
     }
 
     SkData* onEncodePixels(const SkImageInfo&, const void*, size_t) override {
         fDidEncode = true;
         return fFunc();
     }
 
 private:
     SkData* (*fFunc)();
     bool fDidEncode;
@@ skipping 204 matching lines @@
         }
     }
 
     image.reset(nullptr);
     {
         SkBitmap cachedBitmap;
         REPORTER_ASSERT(reporter, !SkBitmapCache::Find(uniqueID, &cachedBitmap));
     }
 }
 #endif