Replace EncodeBitmap with an interface.

dm/DMSerializeTask.cpp

 #include "DMSerializeTask.h"
 #include "DMUtil.h"
 #include "DMWriteTask.h"
 
 #include "SkCommandLineFlags.h"
 #include "SkPicture.h"
 #include "SkPixelRef.h"
 
 DEFINE_bool(serialize, true, "If true, run picture serialization tests via SkPictureData.");
 
 namespace DM {
 
 SerializeTask::SerializeTask(const Task& parent, skiagm::GM* gm, SkBitmap reference)
     : CpuTask(parent)
     , fName(UnderJoin(parent.name().c_str(), "serialize"))
     , fGM(gm)
     , fReference(reference)
     {}
 
 void SerializeTask::draw() {
     SkAutoTUnref<SkPicture> recorded(RecordPicture(fGM.get(), NULL/*no BBH*/));
 
     SkDynamicMemoryWStream wStream;
-    recorded->serialize(&wStream, NULL);
+    recorded->serialize(&wStream);
     SkAutoTUnref<SkStream> rStream(wStream.detachAsStream());
     SkAutoTUnref<SkPicture> reconstructed(SkPicture::CreateFromStream(rStream));
 
     SkBitmap bitmap;
     AllocatePixels(fReference, &bitmap);
     DrawPicture(*reconstructed, &bitmap);
     if (!BitmapsEqual(bitmap, fReference)) {
         this->fail();
         this->spawnChild(SkNEW_ARGS(WriteTask, (*this, "GM", bitmap)));
     }
 }
 
 bool SerializeTask::shouldSkip() const {
     if (fGM->getFlags() & skiagm::GM::kSkipPicture_Flag) {
         return true;
     }
     return !FLAGS_serialize;
 }
 
 }  // namespace DM