More fixes for scoped_refptr operator T* removal.

mojo/system/channel_endpoint.h

 // Copyright 2014 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_CHANNEL_ENDPOINT_H_
 #define MOJO_SYSTEM_CHANNEL_ENDPOINT_H_
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "mojo/system/message_pipe.h"
@@ skipping 85 matching lines @@
 //         running since under the current scheme it wouldn't have a remote ID
 //         yet.]
 //       - Note that even if the local side is closed, it may still receive a
 //         "remove" message from the other side (if the other side is closed
 //         simultaneously, and both sides send "remove" messages). In that
 //         case, it must still remain alive until it receives the "remove
 //         ack" (and it must ack the "remove" message that it received).
 class MOJO_SYSTEM_IMPL_EXPORT ChannelEndpoint
     : public base::RefCountedThreadSafe<ChannelEndpoint> {
  public:
-  ChannelEndpoint(MessagePipe* message_pipe, unsigned port);
+  ChannelEndpoint(const scoped_refptr<MessagePipe>& message_pipe,

[vtl, 2014/09/05 05:41:51]

Why? The original form is fine, and avoids the extra indirection. Moreover, in
the case that the object is passed, this form (as well as passing a
scoped_refptr by value), causes ref count churn, which is expensive.

[dcheng, 2014/09/05 06:01:26]

It's documentation. There's already been some discussion about this pattern in
https://codereview.chromium.org/511323002/,
https://codereview.chromium.org/506153002/, and elsewhere. This is the general
pattern that these conversion CLs have been taking. If this is something you
feel strongly about, I think this would be a good discussion to have on
chromium-dev.
If you care about refcount churn, it appears Channel::AttachMessagePipeEndpoint
already unnecessarily causes refcount churn. And many other places in Chrome.

I've updated this to just pass in the result of .get() when invoking the ctor,
because I'd really like to get the conversion disabled on Linux builds tonight.

+                  unsigned port);
 
  private:
   enum State {
     // Attached, possibly running or not.
     STATE_NORMAL,
     // "Zombie" states:
     // Waiting for |DetachMessagePipeEndpoint()| before removing.
     STATE_WAIT_LOCAL_DETACH,
     // Waiting for a |kSubtypeChannelRemoveMessagePipeEndpointAck| before
     // removing.
@@ skipping 11 matching lines @@
   scoped_refptr<MessagePipe> message_pipe_;
   unsigned port_;
 
   DISALLOW_COPY_AND_ASSIGN(ChannelEndpoint);
 };
 
 }  // namespace system
 }  // namespace mojo
 
 #endif  // MOJO_SYSTEM_CHANNEL_ENDPOINT_H_