Update {virtual,override} to follow C++11 style in src/utils.

src/utils/SkEventTracer.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkAtomics.h"
 #include "SkEventTracer.h"
 #include "SkLazyPtr.h"
 
 class SkDefaultEventTracer : public SkEventTracer {
-    virtual SkEventTracer::Handle
+    SkEventTracer::Handle
         addTraceEvent(char phase,
                       const uint8_t* categoryEnabledFlag,
                       const char* name,
                       uint64_t id,
                       int numArgs,
                       const char** argNames,
                       const uint8_t* argTypes,
                       const uint64_t* argValues,
                       uint8_t flags) override { return 0; }
 
-    virtual void
+    void
         updateTraceEventDuration(const uint8_t* categoryEnabledFlag,
                                  const char* name,
-                                 SkEventTracer::Handle handle) override {};
+                                 SkEventTracer::Handle handle) override {}
 
     const uint8_t* getCategoryGroupEnabled(const char* name) override {
         static uint8_t no = 0;
         return &no;
-    };
-    virtual const char* getCategoryGroupName(
+    }
+    const char* getCategoryGroupName(
       const uint8_t* categoryEnabledFlag) override {
         static const char* dummy = "dummy";
         return dummy;
-    };
+    }
 };
 
 // We prefer gUserTracer if it's been set, otherwise we fall back on gDefaultTracer.
 static SkEventTracer* gUserTracer = nullptr;
 SK_DECLARE_STATIC_LAZY_PTR(SkDefaultEventTracer, gDefaultTracer);
 
 void SkEventTracer::SetInstance(SkEventTracer* tracer) {
     SkASSERT(nullptr == sk_atomic_load(&gUserTracer, sk_memory_order_acquire));
     sk_atomic_store(&gUserTracer, tracer, sk_memory_order_release);
     // An atomic load during process shutdown is probably overkill, but safe overkill.
     atexit([](){ SkDELETE(sk_atomic_load(&gUserTracer, sk_memory_order_acquire)); });
 }
 
 SkEventTracer* SkEventTracer::GetInstance() {
     if (SkEventTracer* tracer = sk_atomic_load(&gUserTracer, sk_memory_order_acquire)) {
         return tracer;
     }
     return gDefaultTracer.get();
 }