shill: Add C++11 override specifier to destructors of derived classes.

BUG=None
TEST=`USE=wimax FEATURES=test emerge-$BOARD platform2`

Change-Id: I88d4e29165869b26924cccb94ac940dc8961c312
Reviewed-on: https://chromium-review.googlesource.com/212267
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Ben Chan <benchan@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
diff --git a/wimax_network_proxy.h b/wimax_network_proxy.h
index 30cd4a6..97ab178 100644
--- a/wimax_network_proxy.h
+++ b/wimax_network_proxy.h
@@ -19,7 +19,7 @@
   // Constructs a WiMaxManager.Network DBus object proxy at |path|.
   WiMaxNetworkProxy(DBus::Connection *connection,
                    const DBus::Path &path);
-  virtual ~WiMaxNetworkProxy();
+  ~WiMaxNetworkProxy() override;
 
   // Inherited from WiMaxNetwokProxyInterface.
   virtual RpcIdentifier path() const;
@@ -37,7 +37,7 @@
                 public DBus::ObjectProxy {
    public:
     Proxy(DBus::Connection *connection, const DBus::Path &path);
-    virtual ~Proxy();
+    ~Proxy() override;
 
     void set_signal_strength_changed_callback(
         const SignalStrengthChangedCallback &callback);