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/mock_virtual_device.h b/mock_virtual_device.h
index c10f246..fa58232 100644
--- a/mock_virtual_device.h
+++ b/mock_virtual_device.h
@@ -22,7 +22,7 @@
                     const std::string &link_name,
                     int interface_index,
                     Technology::Identifier technology);
-  virtual ~MockVirtualDevice();
+  ~MockVirtualDevice() override;
 
   MOCK_METHOD2(Stop,
                void(Error *error, const EnabledStateChangedCallback &callback));