Add a ChannelEndpointClient abstraction.

mojo/edk/system/channel.h

Index: mojo/edk/system/channel.h
diff --git a/mojo/edk/system/channel.h b/mojo/edk/system/channel.h
index 3460a304e3989cd50e015f1bfddc742242aa9554..e0ecc3b7f6b39cdc41d8da685bb30a3f2a5b83ee 100644
--- a/mojo/edk/system/channel.h
+++ b/mojo/edk/system/channel.h
@@ -201,10 +201,10 @@ class MOJO_SYSTEM_IMPL_EXPORT Channel
   // TODO(vtl): This is a layering violation, since |Channel| shouldn't know
   // about |MessagePipe|. However, we can't just hang on to |ChannelEndpoint|s
   // (even if they have a reference to the |MessagePipe|) since their lifetimes
-  // are tied to the "remote" side. When |ChannelEndpoint::OnDisconnect()|
-  // (eventually) results in |ChannelEndpoint::DetachFromMessagePipe()| being
-  // called. We really need to hang on to the "local" side of the message pipe,
-  // to which dispatchers will be "attached".
+  // are tied to the "remote" side. When |ChannelEndpoint::DetachFromChannel()|
+  // (eventually) results in |ChannelEndpoint::DetachFromClient()| being called.
+  // We really need to hang on to the "local" side of the message pipe, to which
+  // dispatchers will be "attached".
   IdToMessagePipeMap incoming_message_pipes_;
   // TODO(vtl): We need to keep track of remote IDs (so that we don't collide
   // if/when we wrap).