Add some missing virtual destructors to base classes.

base/trace_event/trace_event_unittest.cc

Index: base/trace_event/trace_event_unittest.cc
diff --git a/base/trace_event/trace_event_unittest.cc b/base/trace_event/trace_event_unittest.cc
index d6481291fa6f332767404ce8c4aa9dce006ffc37..2112501f0dd1fb10ef279aabece096509b8c8c8e 100644
--- a/base/trace_event/trace_event_unittest.cc
+++ b/base/trace_event/trace_event_unittest.cc
@@ -1020,7 +1020,7 @@ class AfterStateChangeEnabledStateObserver
     : public TraceLog::EnabledStateObserver {
  public:
   AfterStateChangeEnabledStateObserver() {}
-  virtual ~AfterStateChangeEnabledStateObserver() {}
+  ~AfterStateChangeEnabledStateObserver() override {}
 
   // TraceLog::EnabledStateObserver overrides:
   void OnTraceLogEnabled() override {
@@ -1051,7 +1051,7 @@ class SelfRemovingEnabledStateObserver
     : public TraceLog::EnabledStateObserver {
  public:
   SelfRemovingEnabledStateObserver() {}
-  virtual ~SelfRemovingEnabledStateObserver() {}
+  ~SelfRemovingEnabledStateObserver() override {}
 
   // TraceLog::EnabledStateObserver overrides:
   void OnTraceLogEnabled() override {}