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/src/images/SkJPEGImageEncoder.cpp b/src/images/SkJPEGImageEncoder.cpp
index 66b2440..97b8bbc 100644
--- a/src/images/SkJPEGImageEncoder.cpp
+++ b/src/images/SkJPEGImageEncoder.cpp
@@ -5,20 +5,20 @@
  * found in the LICENSE file.
  */
 
+#include "SkImageEncoderPriv.h"
 
-#include "SkImageEncoder.h"
+#include "SkCanvas.h"
 #include "SkColorPriv.h"
 #include "SkDither.h"
+#include "SkJPEGWriteUtility.h"
+#include "SkRect.h"
 #include "SkStream.h"
 #include "SkTemplates.h"
 #include "SkTime.h"
 #include "SkUtils.h"
-#include "SkRect.h"
-#include "SkCanvas.h"
-
 
 #include <stdio.h>
-#include "SkJPEGWriteUtility.h"
+
 extern "C" {
     #include "jpeglib.h"
     #include "jerror.h"
@@ -178,7 +178,7 @@
 ///////////////////////////////////////////////////////////////////////////////
 
 static SkImageEncoder* sk_libjpeg_efactory(SkImageEncoder::Type t) {
-    return (SkImageEncoder::kJPEG_Type == t) ? new SkJPEGImageEncoder : nullptr;
+    return (SkEncodedImageFormat::kJPEG == (SkEncodedImageFormat)t) ? new SkJPEGImageEncoder : nullptr;
 }
 
 static SkImageEncoder_EncodeReg gEReg(sk_libjpeg_efactory);