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/codec/SkRawAdapterCodec.h b/src/codec/SkRawAdapterCodec.h
index b552f2a..8777180 100644
--- a/src/codec/SkRawAdapterCodec.h
+++ b/src/codec/SkRawAdapterCodec.h
@@ -10,7 +10,7 @@
 
 #include "SkAndroidCodec.h"
 #include "SkCodec.h"
-#include "SkEncodedFormat.h"
+#include "SkEncodedImageFormat.h"
 #include "SkRawCodec.h"
 #include "SkStream.h"
 #include "SkTypes.h"