SkImageEncoder: simplify API

(re-land 248ff02 & 2cb6cb7, with changes)

  - Hide SkImageEncoder class in private header.
  - SkImageEncoder::Type becomes SkEncodedImageFormat
  - SkEncodedFormat becomes SkEncodedImageFormat
  - SkImageEncoder static functions replaced with
    single function EncodeImage()
  - utility wrappers for EncodeImage() are in
    sk_tool_utils.h

TODO: remove link-time registration mechanism.
TODO: clean up clients use of API and flip the flag.
TODO: implement EncodeImage() in chromeium/skia/ext

Change-Id: I47d451e50be4d5c6c130869c7fa7c2857243d9f0
Reviewed-on: https://skia-review.googlesource.com/4909
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
Reviewed-on: https://skia-review.googlesource.com/5186
Commit-Queue: Hal Canary <halcanary@google.com>
Reviewed-by: Hal Canary <halcanary@google.com>
diff --git a/tools/skiaserve/Request.cpp b/tools/skiaserve/Request.cpp
index c1b3b25..2064a46 100644
--- a/tools/skiaserve/Request.cpp
+++ b/tools/skiaserve/Request.cpp
@@ -11,6 +11,7 @@
 #include "SkPixelSerializer.h"
 #include "SkPM4fPriv.h"
 #include "picture_utils.h"
+#include "sk_tool_utils.h"
 
 using namespace sk_gpu_test;
 
@@ -117,7 +118,7 @@
 
     SkDynamicMemoryWStream outStream;
 
-    sk_sp<SkPixelSerializer> serializer(SkImageEncoder::CreatePixelSerializer());
+    sk_sp<SkPixelSerializer> serializer = sk_tool_utils::MakePixelSerializer();
     picture->serialize(&outStream, serializer.get());
 
     return outStream.detachAsData();