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/tests/ImageTest.cpp b/tests/ImageTest.cpp
index 18883fe..020e322 100644
--- a/tests/ImageTest.cpp
+++ b/tests/ImageTest.cpp
@@ -26,6 +26,8 @@
 #include "SkUtils.h"
 #include "Test.h"
 
+#include "sk_tool_utils.h"
+
 #if SK_SUPPORT_GPU
 #include "GrGpu.h"
 #endif
@@ -153,7 +155,7 @@
     sk_sp<SkData> data(create_image_data(&info));
     SkBitmap bitmap;
     bitmap.installPixels(info, data->writable_data(), info.minRowBytes());
-    sk_sp<SkData> src(SkImageEncoder::EncodeData(bitmap, SkImageEncoder::kPNG_Type, 100));
+    sk_sp<SkData> src(sk_tool_utils::EncodeImageToData(bitmap, SkEncodedImageFormat::kPNG, 100));
     return SkImage::MakeFromEncoded(std::move(src));
 }
 #if SK_SUPPORT_GPU
@@ -1026,7 +1028,7 @@
     make_all_premul(&bm0);
 
     auto img0 = SkImage::MakeFromBitmap(bm0);
-    sk_sp<SkData> data(img0->encode(SkImageEncoder::kPNG_Type, 100));
+    sk_sp<SkData> data(img0->encode(SkEncodedImageFormat::kPNG, 100));
     auto img1 = SkImage::MakeFromEncoded(data);
 
     SkBitmap bm1;