Convert OVERRIDE -> override and update virtual/final usage in tools/gn/.

tools/gn/loader.h

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef TOOLS_GN_LOADER_H_
 #define TOOLS_GN_LOADER_H_
 
 #include <map>
 #include <set>
 
@@ skipping 64 matching lines @@
   // Callback to emulate InputFileManager::AsyncLoadFile.
   typedef base::Callback<bool(const LocationRange&,
                               const BuildSettings*,
                               const SourceFile&,
                               const base::Callback<void(const ParseNode*)>&,
                               Err*)> AsyncLoadFileCallback;
 
   LoaderImpl(const BuildSettings* build_settings);
 
   // Loader implementation.
-  virtual void Load(const SourceFile& file,
-                    const LocationRange& origin,
-                    const Label& toolchain_name) override;
-  virtual void ToolchainLoaded(const Toolchain* toolchain) override;
-  virtual Label GetDefaultToolchain() const override;
-  virtual const Settings* GetToolchainSettings(
-      const Label& label) const override;
+  void Load(const SourceFile& file,
+            const LocationRange& origin,
+            const Label& toolchain_name) override;
+  void ToolchainLoaded(const Toolchain* toolchain) override;
+  Label GetDefaultToolchain() const override;
+  const Settings* GetToolchainSettings(const Label& label) const override;
 
   // Sets the message loop corresponding to the main thread. By default this
   // class will use the thread active during construction, but there is not
   // a message loop active during construction all the time.
   void set_main_loop(base::MessageLoop* loop) { main_loop_ = loop; }
 
   // The complete callback is called whenever there are no more pending loads.
   // Called on the main thread only. This may be called more than once if the
   // queue is drained, but then more stuff gets added.
   void set_complete_callback(const base::Closure& cb) {
     complete_callback_ = cb;
   }
 
   // This callback is used when the loader finds it wants to load a file.
   void set_async_load_file(const AsyncLoadFileCallback& cb) {
     async_load_file_ = cb;
   }
 
   const Label& default_toolchain_label() const {
     return default_toolchain_label_;
   }
 
  private:
   struct LoadID;
   struct ToolchainRecord;
 
-  virtual ~LoaderImpl();
+  ~LoaderImpl() override;
 
   // Schedules the input file manager to load the given file.
   void ScheduleLoadFile(const Settings* settings,
                         const LocationRange& origin,
                         const SourceFile& file);
   void ScheduleLoadBuildConfig(
       Settings* settings,
       const Scope::KeyValueMap& toolchain_overrides);
 
   // Runs the given file on the background thread. These are called by the
@@ skipping 44 matching lines @@
   const BuildSettings* build_settings_;
   Label default_toolchain_label_;
 
   // Records for the build config file loads.
   // Owning pointers.
   typedef std::map<Label, ToolchainRecord*> ToolchainRecordMap;
   ToolchainRecordMap toolchain_records_;
 };
 
 #endif  // TOOLS_GN_LOADER_H_