Standardize usage of virtual/override/final in chrome/browser/

chrome/browser/metrics/thread_watcher.cc

Index: chrome/browser/metrics/thread_watcher.cc
diff --git a/chrome/browser/metrics/thread_watcher.cc b/chrome/browser/metrics/thread_watcher.cc
index 709ad2b000f2a2a87514483dbdc8f9617f63a95e..e3e36f1fae3d3c04c89bb47fcf00d121df72f787 100644
--- a/chrome/browser/metrics/thread_watcher.cc
+++ b/chrome/browser/metrics/thread_watcher.cc
@@ -932,7 +932,7 @@ class StartupWatchDogThread : public base::Watchdog {
   // Alarm is called if the time expires after an Arm() without someone calling
   // Disarm(). When Alarm goes off, in release mode we get the crash dump
   // without crashing and in debug mode we break into the debugger.
-  virtual void Alarm() override {
+  void Alarm() override {
 #if !defined(NDEBUG)
     StartupHang();
     return;
@@ -978,9 +978,7 @@ class ShutdownWatchDogThread : public base::Watchdog {
 
   // Alarm is called if the time expires after an Arm() without someone calling
   // Disarm(). We crash the browser if this method is called.
-  virtual void Alarm() override {
-    ShutdownHang();
-  }
+  void Alarm() override { ShutdownHang(); }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ShutdownWatchDogThread);