change pixel-serializer to support reencoding existing data

src/image/SkImage.cpp

Index: src/image/SkImage.cpp
diff --git a/src/image/SkImage.cpp b/src/image/SkImage.cpp
index ee76a7ea39ed825e357227fe812cb12c5f3b4e67..240c06e63be94fe3a5c0e6e680dd65105868b2a0 100644
--- a/src/image/SkImage.cpp
+++ b/src/image/SkImage.cpp
@@ -74,6 +74,14 @@ SkShader* SkImage::newShader(SkShader::TileMode tileX,
 }
 
 SkData* SkImage::encode(SkImageEncoder::Type type, int quality) const {
+    SkAutoDataUnref encoded(this->refEncoded());
+    if (encoded) {
+        SkAutoDataUnref reencoded(SkImageEncoder::ReencodeData(encoded, type));
+        if (reencoded) {
+            return reencoded.detach();
+        }
+    }
+
     SkBitmap bm;
     if (as_IB(this)->getROPixels(&bm)) {
         return SkImageEncoder::EncodeData(bm, type, quality);
@@ -85,10 +93,6 @@ namespace {
 
 class DefaultSerializer :  public SkPixelSerializer {
 protected:
-    bool onUseEncodedData(const void *data, size_t len) override {
-        return true;
-    }
-
     SkData* onEncodePixels(const SkImageInfo& info, const void* pixels, size_t rowBytes) override {
         return SkImageEncoder::EncodeData(info, pixels, rowBytes, SkImageEncoder::kPNG_Type, 100);
     }
@@ -101,15 +105,17 @@ SkData* SkImage::encode(SkPixelSerializer* serializer) const {
     SkPixelSerializer* effectiveSerializer = serializer ? serializer : &defaultSerializer;
 
     SkAutoTUnref<SkData> encoded(this->refEncoded());
-    if (encoded && effectiveSerializer->useEncodedData(encoded->data(), encoded->size())) {
-        return encoded.detach();
+    if (encoded) {
+        encoded.reset(effectiveSerializer->reencodeData(encoded));
+        if (encoded) {
+            return encoded.detach();
+        }
     }
 
     SkBitmap bm;
     SkAutoPixmapUnlock apu;
     if (as_IB(this)->getROPixels(&bm) && bm.requestLock(&apu)) {
-        const SkPixmap& pmap = apu.pixmap();
-        return effectiveSerializer->encodePixels(pmap.info(), pmap.addr(), pmap.rowBytes());
+        return effectiveSerializer->encodePixels(apu.pixmap());
     }
 
     return nullptr;