Mojo: Update comment in raw_channel.h.

mojo/system/raw_channel.h

 // Copyright 2013 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.
 
 #ifndef MOJO_SYSTEM_RAW_CHANNEL_H_
 #define MOJO_SYSTEM_RAW_CHANNEL_H_
 
 #include <deque>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/synchronization/lock.h"
 #include "mojo/embedder/scoped_platform_handle.h"
 #include "mojo/system/constants.h"
 #include "mojo/system/message_in_transit.h"
 #include "mojo/system/system_impl_export.h"
 
 namespace base {
 class MessageLoopForIO;
 }
 
 namespace mojo {
 namespace system {
 
-// |RawChannel| is an interface to objects that wrap an OS "pipe". It presents
-// the following interface to users:
+// |RawChannel| is an interface and base class for objects that wrap an OS
+// "pipe". It presents the following interface to users:
 //  - Receives and dispatches messages on an I/O thread (running a
 //    |MessageLoopForIO|.
 //  - Provides a thread-safe way of writing messages (|WriteMessage()|);
 //    writing/queueing messages will not block and is atomic from the point of
 //    view of the caller. If necessary, messages are queued (to be written on
 //    the aforementioned thread).
 //
 // OS-specific implementation subclasses are to be instantiated using the
 // |Create()| static factory method.
 //
@@ skipping 194 matching lines @@
   // are only used/invalidated on the I/O thread.
   base::WeakPtrFactory<RawChannel> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RawChannel);
 };
 
 }  // namespace system
 }  // namespace mojo
 
 #endif  // MOJO_SYSTEM_RAW_CHANNEL_H_