Update {virtual,override} to follow C++11 style in base.

base/trace_event/trace_event.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This header file defines the set of trace_event macros without specifying
 // how the events actually get collected and stored. If you need to expose trace
 // events to some other universe, you can copy-and-paste this file as well as
 // trace_event.h, modifying the macros contained there as necessary for the
 // target platform. The end result is that multiple libraries can funnel events
 // through to a shared trace event collector.
@@ skipping 126 matching lines @@
 // Converting a large data type to a string can be costly. To help with this,
 // the trace framework provides an interface ConvertableToTraceFormat. If you
 // inherit from it and implement the AppendAsTraceFormat method the trace
 // framework will call back to your object to convert a trace output time. This
 // means, if the category for the event is disabled, the conversion will not
 // happen.
 //
 //   class MyData : public base::trace_event::ConvertableToTraceFormat {
 //    public:
 //     MyData() {}
-//     virtual void AppendAsTraceFormat(std::string* out) const override {
+//     void AppendAsTraceFormat(std::string* out) const override {
 //       out->append("{\"foo\":1}");
 //     }
 //    private:
-//     virtual ~MyData() {}
+//     ~MyData() override {}
 //     DISALLOW_COPY_AND_ASSIGN(MyData);
 //   };
 //
 //   TRACE_EVENT1("foo", "bar", "data",
 //                scoped_refptr<ConvertableToTraceFormat>(new MyData()));
 //
 // The trace framework will take ownership if the passed pointer and it will
 // be free'd when the trace buffer is flushed.
 //
 // Note, we only do the conversion when the buffer is flushed, so the provided
@@ skipping 1465 matching lines @@
   const char* name_;
   IDType id_;
 
   DISALLOW_COPY_AND_ASSIGN(TraceScopedTrackableObject);
 };
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_TRACE_EVENT_H_