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

tools/gn/c_include_iterator.h

 // Copyright 2014 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_C_INCLUDE_ITERATOR_H_
 #define TOOLS_GN_C_INCLUDE_ITERATOR_H_
 
 #include "base/basictypes.h"
 #include "base/strings/string_piece.h"
 
 class InputFile;
 class LocationRange;
 
 // Iterates through #includes in C source and header files.
 //
 // This only returns includes we want to check, which is user includes with
 // double-quotes: #include "..."
 class CIncludeIterator {
  public:
   // The InputFile pointed to must outlive this class.
-  CIncludeIterator(const InputFile* input);
+  explicit CIncludeIterator(const InputFile* input);
   ~CIncludeIterator();
 
   // Fills in the string with the contents of the next include, and the
   // location with where it came from, and returns true, or returns false if
   // there are no more includes.
   bool GetNextIncludeString(base::StringPiece* out, LocationRange* location);
 
   // Maximum numbef of non-includes we'll tolerate before giving up. This does
   // not count comments or preprocessor.
   static const int kMaxNonIncludeLines;
@@ skipping 14 matching lines @@
   int line_number_;  // One-based. Indicates the last line we read.
 
   // Number of lines we've processed since seeing the last include (or the
   // beginning of the file) with some exceptions.
   int lines_since_last_include_;
 
   DISALLOW_COPY_AND_ASSIGN(CIncludeIterator);
 };
 
 #endif  // TOOLS_GN_INCLUDE_ITERATOR_H_