Add SkCodec, including PNG implementation.

src/codec/SkCodec.cpp

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkCodec.h"
+#include "SkData.h"
+#include "SkCodec_libpng.h"
+#include "SkStream.h"
+
+SkCodec* SkCodec::NewFromStream(SkStream* stream) {
+    if (!stream) {
+        return NULL;
+    }
+    SkAutoTDelete<SkStream> streamDeleter(stream);
+    const bool isPng = SkPngCodec::IsPng(stream);
+    // TODO: Avoid rewinding.
+    if (!stream->rewind()) {
+        return NULL;
+    }
+    if (isPng) {
+        streamDeleter.detach();
+        return SkPngCodec::NewFromStream(stream);
+    }
+    // TODO: Check other image types.
+    return NULL;
+}
+
+SkCodec* SkCodec::NewFromData(SkData* data) {
+    if (!data) {
+        return NULL;
+    }
+    return NewFromStream(SkNEW_ARGS(SkMemoryStream, (data)));
+}
+
+SkCodec::SkCodec(const SkImageInfo& info, SkStream* stream)
+    : fInfo(info)
+    , fStream(stream)
+    , fNeedsRewind(false)
+{}
+
+bool SkCodec::rewindIfNeeded() {
+    // Store the value of fNeedsRewind so we can update it. Next read will
+    // require a rewind.
+    const bool neededRewind = fNeedsRewind;
+    fNeedsRewind = true;
+    return !neededRewind || fStream->rewind();
+}