Standardize usage of virtual/override/final in base/

base/debug/trace_event_synthetic_delay_unittest.cc

Index: base/debug/trace_event_synthetic_delay_unittest.cc
diff --git a/base/debug/trace_event_synthetic_delay_unittest.cc b/base/debug/trace_event_synthetic_delay_unittest.cc
index 124706fb56212872e92acf3470d13ce6fdfd3b54..60e4d20368eb6ab41eb24dc40cad22f411c3732a 100644
--- a/base/debug/trace_event_synthetic_delay_unittest.cc
+++ b/base/debug/trace_event_synthetic_delay_unittest.cc
@@ -26,7 +26,7 @@ class TraceEventSyntheticDelayTest : public testing::Test,
   }
 
   // TraceEventSyntheticDelayClock implementation.
-  virtual base::TimeTicks Now() override {
+  base::TimeTicks Now() override {
     AdvanceTime(base::TimeDelta::FromMilliseconds(kShortDurationMs / 10));
     return now_;
   }