change pixel-serializer to support reencoding existing data

tools/sk_tool_utils.h

Index: tools/sk_tool_utils.h
diff --git a/tools/sk_tool_utils.h b/tools/sk_tool_utils.h
index b20c60ba7632d9ed98f6f6cdd84f47e06ac4c99f..085489a6d96c8689080c60e93b03a04452cb6734 100644
--- a/tools/sk_tool_utils.h
+++ b/tools/sk_tool_utils.h
@@ -115,11 +115,8 @@ namespace sk_tool_utils {
     // used.
     class PngPixelSerializer : public SkPixelSerializer {
     public:
-        bool onUseEncodedData(const void*, size_t) 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);
+        SkData* onEncodePixels(const SkPixmap& pmap) override {
+            return SkImageEncoder::EncodeData(pmap, SkImageEncoder::kPNG_Type, 100);
         }
     };