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/bench/GLBench.cpp b/bench/GLBench.cpp
index a39edee..cb824da 100644
--- a/bench/GLBench.cpp
+++ b/bench/GLBench.cpp
@@ -15,6 +15,8 @@
 #include "SkSLCompiler.h"
 #include <stdio.h>
 
+#include "sk_tool_utils.h"
+
 const GrGLContext* GLBench::getGLContext(SkCanvas* canvas) {
     // This bench exclusively tests GL calls directly
     if (nullptr == canvas->getGrContext()) {
@@ -181,7 +183,7 @@
 
     bm.setPixels(readback.get());
 
-    if (!SkImageEncoder::EncodeFile(filename, bm, SkImageEncoder::kPNG_Type, 100)) {
+    if (!sk_tool_utils::EncodeImageToFile(filename, bm, SkEncodedImageFormat::kPNG, 100)) {
         SkDebugf("------ failed to encode %s\n", filename);
         remove(filename);   // remove any partial file
         return;