dbus: don't fail when reconnecting object signals

dbus/object_proxy.h

 // Copyright (c) 2012 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 DBUS_OBJECT_PROXY_H_
 #define DBUS_OBJECT_PROXY_H_
 #pragma once
 
 #include <dbus/dbus.h>
 
@@ skipping 11 matching lines @@
 
 class Bus;
 class MethodCall;
 class Response;
 class Signal;
 
 // ObjectProxy is used to communicate with remote objects, mainly for
 // calling methods of these objects.
 //
 // ObjectProxy is a ref counted object, to ensure that |this| of the
-// object is is alive when callbacks referencing |this| are called.
+// object is is alive when callbacks referencing |this| are called; the
+// bus always holds at least one of those references so object proxies
+// always last as long as the bus that created them.
 class ObjectProxy : public base::RefCountedThreadSafe<ObjectProxy> {
  public:
   // Client code should use Bus::GetObjectProxy() or
   // Bus::GetObjectProxyWithOptions() instead of this constructor.
   ObjectProxy(Bus* bus,
               const std::string& service_name,
               const ObjectPath& object_path,
               int options);
 
   // Options to be OR-ed together when calling Bus::GetObjectProxyWithOptions().
@@ skipping 46 matching lines @@
   //
   // If the method call is successful, a pointer to Response object will
   // be passed to the callback. If unsuccessful, NULL will be passed to
   // the callback.
   //
   // Must be called in the origin thread.
   virtual void CallMethod(MethodCall* method_call,
                           int timeout_ms,
                           ResponseCallback callback);
 
-  // Requests to connect to the signal from the remote object.
+  // Requests to connect to the signal from the remote object, replacing
+  // any previous |signal_callback| connected to that signal.
   //
   // |signal_callback| will be called in the origin thread, when the
   // signal is received from the remote object. As it's called in the
   // origin thread, |signal_callback| can safely reference objects in the
   // origin thread (i.e. UI thread in most cases).
   //
   // |on_connected_callback| is called when the object proxy is connected
   // to the signal, or failed to be connected, in the origin thread.
   //
   // Must be called in the origin thread.
@@ skipping 100 matching lines @@
   std::set<std::string> match_rules_;
 
   const bool ignore_service_unknown_errors_;
 
   DISALLOW_COPY_AND_ASSIGN(ObjectProxy);
 };
 
 }  // namespace dbus
 
 #endif  // DBUS_OBJECT_PROXY_H_