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_portal_detector.h b/mock_portal_detector.h
index 2370d12..c9349db 100644
--- a/mock_portal_detector.h
+++ b/mock_portal_detector.h
@@ -17,7 +17,7 @@
 class MockPortalDetector : public PortalDetector {
  public:
   explicit MockPortalDetector(ConnectionRefPtr connection);
-  virtual ~MockPortalDetector();
+  ~MockPortalDetector() override;
 
   MOCK_METHOD1(Start, bool(const std::string &));
   MOCK_METHOD2(StartAfterDelay, bool(const std::string &, int delay_seconds));