chromeos: Add out-of-line copy ctors for complex classes.

chromeos/dbus/audio_node.h

Index: chromeos/dbus/audio_node.h
diff --git a/chromeos/dbus/audio_node.h b/chromeos/dbus/audio_node.h
index 68e21092a3e6ebe1933a0e1874baaa7336260adb..d6f90e523cb6eded89b8a66f715970435dac4735 100644
--- a/chromeos/dbus/audio_node.h
+++ b/chromeos/dbus/audio_node.h
@@ -36,6 +36,7 @@ struct CHROMEOS_EXPORT AudioNode {
             std::string name,
             bool active,
             uint64_t plugged_time);
+  AudioNode(const AudioNode& other);
   ~AudioNode();
   std::string ToString() const;
 };