SkImageEncoder: simplify API

  - 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

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4909

Change-Id: Ib48b31fdc05cf23cda7f56ebfd67c841c149ce70
Reviewed-on: https://skia-review.googlesource.com/4909
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
diff --git a/tools/skdiff/skdiff_utils.cpp b/tools/skdiff/skdiff_utils.cpp
index f788ec8..f8eed90 100644
--- a/tools/skdiff/skdiff_utils.cpp
+++ b/tools/skdiff/skdiff_utils.cpp
@@ -6,6 +6,7 @@
  */
 #include "skdiff.h"
 #include "skdiff_utils.h"
+#include "sk_tool_utils.h"
 #include "SkBitmap.h"
 #include "SkCodec.h"
 #include "SkData.h"
@@ -82,8 +83,8 @@
     SkBitmap copy;
     bitmap.copyTo(&copy, kN32_SkColorType);
     force_all_opaque(copy);
-    return SkImageEncoder::EncodeFile(path.c_str(), copy,
-                                      SkImageEncoder::kPNG_Type, 100);
+    return sk_tool_utils::EncodeImageToFile(path.c_str(), copy,
+                                      SkEncodedImageFormat::kPNG, 100);
 }
 
 /// Return a copy of the "input" string, within which we have replaced all instances