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

tools/gn/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_TARGET_GENERATOR_H_
 #define TOOLS_GN_TARGET_GENERATOR_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 12 matching lines @@
 // Fills the variables in a Target object from a Scope (the result of a script
 // execution). Target-type-specific derivations of this class will be used
 // for each different type of function call. This class implements the common
 // behavior.
 class TargetGenerator {
  public:
   TargetGenerator(Target* target,
                   Scope* scope,
                   const FunctionCallNode* function_call,
                   Err* err);
-  ~TargetGenerator();
+  virtual ~TargetGenerator();
 
   void Run();
 
   // The function call is the parse tree node that invoked the target.
   // err() will be set on failure.
   static void GenerateTarget(Scope* scope,
                              const FunctionCallNode* function_call,
                              const std::vector<Value>& args,
                              const std::string& output_type,
                              Err* err);
@@ skipping 34 matching lines @@
   bool FillGenericConfigs(const char* var_name,
                           UniqueVector<LabelConfigPair>* dest);
   bool FillGenericDeps(const char* var_name, LabelTargetVector* dest);
 
   bool FillForwardDependentConfigs();
 
   DISALLOW_COPY_AND_ASSIGN(TargetGenerator);
 };
 
 #endif  // TOOLS_GN_TARGET_GENERATOR_H_