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/modem_manager.h b/modem_manager.h
index cebd30c..51ae398 100644
--- a/modem_manager.h
+++ b/modem_manager.h
@@ -111,7 +111,7 @@
                       const std::string &path,
                       ModemInfo *modem_info);
 
-  virtual ~ModemManagerClassic();
+  ~ModemManagerClassic() override;
 
   // Called by our dbus proxy
   void OnDeviceAdded(const std::string &path);
@@ -139,7 +139,7 @@
                 const std::string &path,
                 ModemInfo *modem_info);
 
-  virtual ~ModemManager1();
+  ~ModemManager1() override;
 
  protected:
   void AddModem1(const std::string &path,