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

tools/gn/input_file_manager.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_INPUT_FILE_MANAGER_H_
 #define TOOLS_GN_INPUT_FILE_MANAGER_H_
 
 #include <set>
 #include <utility>
 #include <vector>
@@ skipping 76 matching lines @@
   // Does not count dynamic input.
   int GetInputFileCount() const;
 
   // Fills the vector with all input files.
   void GetAllPhysicalInputFileNames(std::vector<base::FilePath>* result) const;
 
  private:
   friend class base::RefCountedThreadSafe<InputFileManager>;
 
   struct InputFileData {
-    InputFileData(const SourceFile& file_name);
+    explicit InputFileData(const SourceFile& file_name);
     ~InputFileData();
 
     // Don't touch this outside the lock until it's marked loaded.
     InputFile file;
 
     bool loaded;
 
     bool sync_invocation;
 
     // Lists all invocations that need to be executed when the file completes
@@ skipping 39 matching lines @@
   //
   // See AddDynamicInput().
   //
   // Owning pointers.
   std::vector<InputFileData*> dynamic_inputs_;
 
   DISALLOW_COPY_AND_ASSIGN(InputFileManager);
 };
 
 #endif  // TOOLS_GN_INPUT_FILE_MANAGER_H_