Remove image decoder and encoder autoregistration

src/images/SkImageDecoder_libgif.cpp

Index: src/images/SkImageDecoder_libgif.cpp
diff --git a/src/images/SkImageDecoder_libgif.cpp b/src/images/SkImageDecoder_libgif.cpp
index 81071c95158be16957e20d3fdfb0ad3554ade7ce..f3a267c7fdf430c8763609c12963292cf93e9181 100644
--- a/src/images/SkImageDecoder_libgif.cpp
+++ b/src/images/SkImageDecoder_libgif.cpp
@@ -5,10 +5,11 @@
  * found in the LICENSE file.
  */
 
+#include "SkImageDecoder_libgif.h"
+
 #include "SkColor.h"
 #include "SkColorPriv.h"
 #include "SkColorTable.h"
-#include "SkImageDecoder.h"
 #include "SkRTConf.h"
 #include "SkScaledBitmapSampler.h"
 #include "SkStream.h"
@@ -501,36 +502,21 @@ bool SkGIFImageDecoder::onDecode(SkStream* sk_stream, SkBitmap* bm, Mode mode) {
     return true;
 }
 
-///////////////////////////////////////////////////////////////////////////////
-DEFINE_DECODER_CREATOR(GIFImageDecoder);
-///////////////////////////////////////////////////////////////////////////////
-
-static bool is_gif(SkStreamRewindable* stream) {
+SkImageDecoder::Format SkDetectFormatGIFImageDecoder(SkStreamRewindable* stream) {
     char buf[GIF_STAMP_LEN];
     if (stream->read(buf, GIF_STAMP_LEN) == GIF_STAMP_LEN) {
         if (memcmp(GIF_STAMP,   buf, GIF_STAMP_LEN) == 0 ||
                 memcmp(GIF87_STAMP, buf, GIF_STAMP_LEN) == 0 ||
                 memcmp(GIF89_STAMP, buf, GIF_STAMP_LEN) == 0) {
-            return true;
+            return SkImageDecoder::kGIF_Format;
         }
     }
-    return false;
+    return SkImageDecoder::kUnknown_Format;
 }
 
-static SkImageDecoder* sk_libgif_dfactory(SkStreamRewindable* stream) {
-    if (is_gif(stream)) {
+SkImageDecoder* SkCreateGIFImageDecoder(SkStreamRewindable* stream) {
+    if (SkDetectFormatGIFImageDecoder(stream) == SkImageDecoder::kGIF_Format) {
         return SkNEW(SkGIFImageDecoder);
     }
     return NULL;
 }
-
-static SkImageDecoder_DecodeReg gReg(sk_libgif_dfactory);
-
-static SkImageDecoder::Format get_format_gif(SkStreamRewindable* stream) {
-    if (is_gif(stream)) {
-        return SkImageDecoder::kGIF_Format;
-    }
-    return SkImageDecoder::kUnknown_Format;
-}
-
-static SkImageDecoder_FormatReg gFormatReg(get_format_gif);