change pixel-serializer to support reencoding existing data

src/images/SkImageEncoder.cpp

Index: src/images/SkImageEncoder.cpp
diff --git a/src/images/SkImageEncoder.cpp b/src/images/SkImageEncoder.cpp
index cc1b73baa52150de72f20c1543634503d83770f9..4ad12c84cd60d7b9701e4b0ea92808150422eb3a 100644
--- a/src/images/SkImageEncoder.cpp
+++ b/src/images/SkImageEncoder.cpp
@@ -60,3 +60,13 @@ SkData* SkImageEncoder::EncodeData(const SkImageInfo& info, const void* pixels,
     SkAutoTDelete<SkImageEncoder> enc(SkImageEncoder::Create(t));
     return enc.get() ? enc.get()->encodeData(bm, quality) : nullptr;
 }
+
+SkData* SkImageEncoder::EncodeData(const SkPixmap& pmap, Type t, int quality) {
+    return EncodeData(pmap.info(), pmap.addr(), pmap.rowBytes(), t, quality);
+}
+
+SkData* SkImageEncoder::ReencodeData(SkData* encoded, Type t) {
+    SkAutoTDelete<SkImageEncoder> enc(SkImageEncoder::Create(t));
+    return enc.get() ? enc.get()->onReencodeData(encoded) : nullptr;
+}
+