Mojo: Update comment in raw_channel.h.

mojo/system/raw_channel.h

Index: mojo/system/raw_channel.h
diff --git a/mojo/system/raw_channel.h b/mojo/system/raw_channel.h
index 8d8d23519a2bbf6876a01f62d92b92b632abe191..2eb28f67ac474adc97779389435dc57bdf1c6cae 100644
--- a/mojo/system/raw_channel.h
+++ b/mojo/system/raw_channel.h
@@ -24,8 +24,8 @@ 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()|);