Add a new incremental parsing API

Change-Id: I6b921766836d58df0281fb23b2add3f62a478e14

webm_parser/src/parser_utils.cc

@@ -0,0 +1,34 @@
+// Copyright (c) 2016 The WebM project authors. All Rights Reserved.
+//
+// Use of this source code is governed by a BSD-style license
+// that can be found in the LICENSE file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS.  All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
+#include "src/parser_utils.h"
+
+#include <cassert>
+#include <cstdint>
+
+#include "webm/reader.h"
+#include "webm/status.h"
+
+namespace webm {
+
+Status ReadByte(Reader* reader, std::uint8_t* byte) {
+  assert(reader != nullptr);
+  assert(byte != nullptr);
+
+  std::uint64_t num_bytes_read;
+  const Status status = reader->Read(1, byte, &num_bytes_read);
+
+  if (!status.completed_ok()) {
+    assert(num_bytes_read == 0);
+  } else {
+    assert(num_bytes_read == 1);
+  }
+
+  return status;
+}
+
+}  // namespace webm