Add `chunk` segmented data library.

common/chunkstream/chunk.go

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package chunkstream
+
+// Chunk wraps a fixed-size byte buffer. It is the primary interface used by
+// the chunk library.
+//
+// A Chunk reference should be released once the user is finished with it. After
+// being released, it may no longer be accessed.
+type Chunk interface {
+        // Bytes returns the underlying byte slice contained by this Chunk.
+        Bytes() []byte
+
+        // Release releases the Chunk. After being released, a Chunk's methods may no
+        // longer be used.
+        Release()
+}