tools/gn: Fix errors found by Facebook's flint tool.

tools/gn/binary_target_generator.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_BINARY_TARGET_GENERATOR_H_
 #define TOOLS_GN_BINARY_TARGET_GENERATOR_H_
 
 #include "base/macros.h"
 #include "tools/gn/target_generator.h"
 
 // Populates a Target with the values from a binary rule (executable, shared
 // library, or static library).
 class BinaryTargetGenerator : public TargetGenerator {
  public:
   BinaryTargetGenerator(Target* target,
                         Scope* scope,
                         const FunctionCallNode* function_call,
                         Target::OutputType type,
                         Err* err);
-  virtual ~BinaryTargetGenerator();
+  ~BinaryTargetGenerator() override;
 
  protected:
   void DoRun() override;
 
  private:
   bool FillCompleteStaticLib();
   bool FillOutputName();
   bool FillOutputExtension();
   bool FillAllowCircularIncludesFrom();
 
   Target::OutputType output_type_;
 
   DISALLOW_COPY_AND_ASSIGN(BinaryTargetGenerator);
 };
 
 #endif  // TOOLS_GN_BINARY_TARGET_GENERATOR_H_