Standardize usage of virtual/override/final in base/

base/debug/trace_event_memory.cc

Index: base/debug/trace_event_memory.cc
diff --git a/base/debug/trace_event_memory.cc b/base/debug/trace_event_memory.cc
index 5cb09087f57fa404eedee214ef9c80ec3069d0aa..28318654750950df5f179aec0f7fa25c26165f7e 100644
--- a/base/debug/trace_event_memory.cc
+++ b/base/debug/trace_event_memory.cc
@@ -33,12 +33,12 @@ class MemoryDumpHolder : public base::debug::ConvertableToTraceFormat {
   explicit MemoryDumpHolder(char* dump) : dump_(dump) {}
 
   // base::debug::ConvertableToTraceFormat overrides:
-  virtual void AppendAsTraceFormat(std::string* out) const override {
+  void AppendAsTraceFormat(std::string* out) const override {
     AppendHeapProfileAsTraceFormat(dump_, out);
   }
 
  private:
-  virtual ~MemoryDumpHolder() { free(dump_); }
+  ~MemoryDumpHolder() override { free(dump_); }
 
   char* dump_;