Revert of Delete SkImageDecoder

src/images/SkImageDecoder_FactoryRegistrar.cpp

+/*
+ * Copyright 2013 The Android Open Source Project
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkErrorInternals.h"
+#include "SkImageDecoder.h"
+#include "SkStream.h"
+#include "SkTRegistry.h"
+
+// This file is used for registration of SkImageDecoders. It also holds a function
+// for checking all the the registered SkImageDecoders for one that matches an
+// input SkStreamRewindable.
+
+template SkImageDecoder_DecodeReg* SkImageDecoder_DecodeReg::gHead;
+
+SkImageDecoder* image_decoder_from_stream(SkStreamRewindable*);
+
+SkImageDecoder* image_decoder_from_stream(SkStreamRewindable* stream) {
+    SkImageDecoder* codec = nullptr;
+    const SkImageDecoder_DecodeReg* curr = SkImageDecoder_DecodeReg::Head();
+    while (curr) {
+        codec = curr->factory()(stream);
+        // we rewind here, because we promise later when we call "decode", that
+        // the stream will be at its beginning.
+        bool rewindSuceeded = stream->rewind();
+
+        // our image decoder's require that rewind is supported so we fail early
+        // if we are given a stream that does not support rewinding.
+        if (!rewindSuceeded) {
+            SkDEBUGF(("Unable to rewind the image stream."));
+            delete codec;
+            return nullptr;
+        }
+
+        if (codec) {
+            return codec;
+        }
+        curr = curr->next();
+    }
+    return nullptr;
+}
+
+template SkImageDecoder_FormatReg* SkImageDecoder_FormatReg::gHead;
+
+SkImageDecoder::Format SkImageDecoder::GetStreamFormat(SkStreamRewindable* stream) {
+    const SkImageDecoder_FormatReg* curr = SkImageDecoder_FormatReg::Head();
+    while (curr != nullptr) {
+        Format format = curr->factory()(stream);
+        if (!stream->rewind()) {
+            SkErrorInternals::SetError(kInvalidOperation_SkError,
+                                       "Unable to rewind the image stream\n");
+            return kUnknown_Format;
+        }
+        if (format != kUnknown_Format) {
+            return format;
+        }
+        curr = curr->next();
+    }
+    return kUnknown_Format;
+}