Add missing virtual destructors to tests.

Change-Id: I916b1e646d9fe142d3483039eb6cc72464529832
diff --git a/test/borders_test.cc b/test/borders_test.cc
index 5071541..b30be45 100644
--- a/test/borders_test.cc
+++ b/test/borders_test.cc
@@ -21,6 +21,7 @@
     public ::libvpx_test::CodecTestWithParam<libvpx_test::TestMode> {
  protected:
   BordersTest() : EncoderTest(GET_PARAM(0)) {}
+  virtual ~BordersTest() {}
 
   virtual void SetUp() {
     InitializeConfig();