Stop deleting ObjectProxy::OnPendingCallIsCompleteData manually

Instead, let libdbus handle it.
This also makes it easier to implement method call cancellation.

BUG=471175

Review URL: https://codereview.chromium.org/1032263002

Cr-Commit-Position: refs/heads/master@{#322746}

dbus/object_proxy.cc

@@ -275,7 +275,7 @@ void ObjectProxy::StartAsyncMethodCall(int timeout_ms,
       pending_call,
       &ObjectProxy::OnPendingCallIsCompleteThunk,
       data,
-      NULL);
+      &DeleteVoidPointer<OnPendingCallIsCompleteData>);
   CHECK(success) << "Unable to allocate memory";
   dbus_pending_call_unref(pending_call);
 
@@ -367,7 +367,6 @@ void ObjectProxy::OnPendingCallIsCompleteThunk(DBusPendingCall* pending_call,
                                 data->response_callback,
                                 data->error_callback,
                                 data->start_time);
-  delete data;
 }
 
 bool ObjectProxy::ConnectToNameOwnerChangedSignal() {

dbus/util.h

@@ -23,6 +23,13 @@ CHROME_DBUS_EXPORT std::string GetAbsoluteMemberName(
     const std::string& interface_name,
     const std::string& member_name);
 
+// Similar to base::DeletePointer, but takes void* as an argument.
+// Used as DBusFreeFunction.
+template<typename T>
+void DeleteVoidPointer(void* memory) {
+  delete static_cast<T*>(memory);
+}
+
 }  // namespace dbus
 
 #endif  // DBUS_UTIL_H_