Remove image decoder and encoder autoregistration

src/images/SkImageDecoder_libpng.cpp

Index: src/images/SkImageDecoder_libpng.cpp
diff --git a/src/images/SkImageDecoder_libpng.cpp b/src/images/SkImageDecoder_libpng.cpp
index 0890eaacaffacf8e4af3af71d38726c493294ba4..cff9d8bc655b65e0c8197a99d3febd450ef574dd 100644
--- a/src/images/SkImageDecoder_libpng.cpp
+++ b/src/images/SkImageDecoder_libpng.cpp
@@ -5,8 +5,7 @@
  * found in the LICENSE file.
  */
 
-#include "SkImageDecoder.h"
-#include "SkImageEncoder.h"
+#include "SkImageDecoder_libpng.h"
 #include "SkColor.h"
 #include "SkColorPriv.h"
 #include "SkDither.h"
@@ -1248,38 +1247,22 @@ bool SkPNGImageEncoder::doEncode(SkWStream* stream, const SkBitmap& bitmap,
     return true;
 }
 
-///////////////////////////////////////////////////////////////////////////////
-DEFINE_DECODER_CREATOR(PNGImageDecoder);
-DEFINE_ENCODER_CREATOR(PNGImageEncoder);
-///////////////////////////////////////////////////////////////////////////////
-
-static bool is_png(SkStreamRewindable* stream) {
+SkImageDecoder::Format SkDetectFormatPNGImageDecoder(SkStreamRewindable* stream) {
     char buf[PNG_BYTES_TO_CHECK];
-    if (stream->read(buf, PNG_BYTES_TO_CHECK) == PNG_BYTES_TO_CHECK &&
-        !png_sig_cmp((png_bytep) buf, (png_size_t)0, PNG_BYTES_TO_CHECK)) {
-        return true;
-    }
-    return false;
-}
-
-SkImageDecoder* sk_libpng_dfactory(SkStreamRewindable* stream) {
-    if (is_png(stream)) {
-        return SkNEW(SkPNGImageDecoder);
+    if (stream->read(buf, PNG_BYTES_TO_CHECK) == PNG_BYTES_TO_CHECK) {
+        if (0 == png_sig_cmp((png_bytep) buf, (png_size_t)0, PNG_BYTES_TO_CHECK)) {
+            return SkImageDecoder::kPNG_Format;
+        }
     }
-    return NULL;
+    return SkImageDecoder::kUnknown_Format;
 }
 
-static SkImageDecoder::Format get_format_png(SkStreamRewindable* stream) {
-    if (is_png(stream)) {
-        return SkImageDecoder::kPNG_Format;
-    }
-    return SkImageDecoder::kUnknown_Format;
+SkImageDecoder* SkCreatePNGImageDecoder(SkImageDecoder::Format format) {
+    SkASSERT(SkImageDecoder::kPNG_Format == format);
+    return SkNEW(SkPNGImageDecoder);
 }
 
-SkImageEncoder* sk_libpng_efactory(SkImageEncoder::Type t) {
+SkImageEncoder* SkCreatePNGImageEncoder(SkImageEncoder::Type t) {
     return (SkImageEncoder::kPNG_Type == t) ? SkNEW(SkPNGImageEncoder) : NULL;
 }
 
-static SkImageDecoder_DecodeReg gDReg(sk_libpng_dfactory);
-static SkImageDecoder_FormatReg gFormatReg(get_format_png);
-static SkImageEncoder_EncodeReg gEReg(sk_libpng_efactory);