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

chrome/browser/web_resource/json_asynchronous_unpacker.cc

Index: chrome/browser/web_resource/json_asynchronous_unpacker.cc
diff --git a/chrome/browser/web_resource/json_asynchronous_unpacker.cc b/chrome/browser/web_resource/json_asynchronous_unpacker.cc
index b65feca9b4b5b479bcd9d8527f5ac4076778eeaa..b64d3a16ee64d998786dcae3ce56ede5cc3e3af7 100644
--- a/chrome/browser/web_resource/json_asynchronous_unpacker.cc
+++ b/chrome/browser/web_resource/json_asynchronous_unpacker.cc
@@ -29,7 +29,7 @@ class JSONAsynchronousUnpackerImpl
       got_response_(false) {
   }
 
-  virtual void Start(const std::string& json_data) override {
+  void Start(const std::string& json_data) override {
     AddRef();  // balanced in Cleanup.
 
     BrowserThread::ID thread_id;
@@ -42,10 +42,10 @@ class JSONAsynchronousUnpackerImpl
   }
 
  private:
-  virtual ~JSONAsynchronousUnpackerImpl() {}
+  ~JSONAsynchronousUnpackerImpl() override {}
 
   // UtilityProcessHostClient.
-  virtual bool OnMessageReceived(const IPC::Message& message) override {
+  bool OnMessageReceived(const IPC::Message& message) override {
     bool handled = true;
     IPC_BEGIN_MESSAGE_MAP(JSONAsynchronousUnpackerImpl, message)
       IPC_MESSAGE_HANDLER(ChromeUtilityHostMsg_UnpackWebResource_Succeeded,
@@ -57,7 +57,7 @@ class JSONAsynchronousUnpackerImpl
     return handled;
   }
 
-  virtual void OnProcessCrashed(int exit_code) override {
+  void OnProcessCrashed(int exit_code) override {
     if (got_response_)
       return;