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

content/browser/device_monitor_mac.mm

Index: content/browser/device_monitor_mac.mm
diff --git a/content/browser/device_monitor_mac.mm b/content/browser/device_monitor_mac.mm
index cbe0bedd763b2866b71f525e8c964198969b8aa1..f33c09752ea1ebcb5db7b0c57899dedc0c7436bd 100644
--- a/content/browser/device_monitor_mac.mm
+++ b/content/browser/device_monitor_mac.mm
@@ -136,9 +136,10 @@ void DeviceMonitorMacImpl::ConsolidateDevicesListAndNotify(
 class QTKitMonitorImpl : public DeviceMonitorMacImpl {
  public:
   explicit QTKitMonitorImpl(content::DeviceMonitorMac* monitor);
-  virtual ~QTKitMonitorImpl();
+  ~QTKitMonitorImpl() override;
+
+  void OnDeviceChanged() override;
 
-  virtual void OnDeviceChanged() override;
  private:
   void CountDevices();
   void OnAttributeChanged(NSNotification* notification);
@@ -377,9 +378,9 @@ class AVFoundationMonitorImpl : public DeviceMonitorMacImpl {
   AVFoundationMonitorImpl(
       content::DeviceMonitorMac* monitor,
       const scoped_refptr<base::SingleThreadTaskRunner>& device_task_runner);
-  virtual ~AVFoundationMonitorImpl();
+  ~AVFoundationMonitorImpl() override;
 
-  virtual void OnDeviceChanged() override;
+  void OnDeviceChanged() override;
 
  private:
   // {Video,AudioInput}DeviceManager's "Device" thread task runner used for