Standardize usage of virtual/override/final in content/

content/plugin/plugin_thread.cc

Index: content/plugin/plugin_thread.cc
diff --git a/content/plugin/plugin_thread.cc b/content/plugin/plugin_thread.cc
index 2663b0f2265ff2248dd15f0a6523539337fcb8e1..e51e39b9a63bf0724916200d24041f7233dcbacd 100644
--- a/content/plugin/plugin_thread.cc
+++ b/content/plugin/plugin_thread.cc
@@ -39,10 +39,10 @@ class EnsureTerminateMessageFilter : public IPC::MessageFilter {
   EnsureTerminateMessageFilter() {}
 
  protected:
-  virtual ~EnsureTerminateMessageFilter() {}
+  ~EnsureTerminateMessageFilter() override {}
 
   // IPC::MessageFilter:
-  virtual void OnChannelError() override {
+  void OnChannelError() override {
     // How long we wait before forcibly shutting down the process.
     const base::TimeDelta kPluginProcessTerminateTimeout =
         base::TimeDelta::FromSeconds(3);