gn: attach comments to parse tree

tools/gn/tokenizer.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_TOKENIZER_H_
 #define TOOLS_GN_TOKENIZER_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
@@ skipping 34 matching lines @@
   // InputFile must outlive the tokenizer and all generated tokens.
   explicit Tokenizer(const InputFile* input_file, Err* err);
   ~Tokenizer();
 
   std::vector<Token> Run();
 
   void AdvanceToNextToken();
   Token::Type ClassifyCurrent() const;
   void AdvanceToEndOfToken(const Location& location, Token::Type type);
 
+  // Whether from this location back to the beginning of the line is only
+  // whitespace. |location| should be the first character of the token to be
+  // checked.
+  bool AtStartOfLine(size_t location) const;
+
   bool IsCurrentWhitespace() const;
   bool IsCurrentNewline() const;
   bool IsCurrentStringTerminator(char quote_char) const;
 
   bool CanIncrement() const { return cur_ < input_.size(); }
 
   // Increments the current location by one.
   void Advance();
 
   // Returns the current character in the file as a location.
@@ skipping 15 matching lines @@
   Err* err_;
   size_t cur_;  // Byte offset into input buffer.
 
   int line_number_;
   int char_in_line_;
 
   DISALLOW_COPY_AND_ASSIGN(Tokenizer);
 };
 
 #endif  // TOOLS_GN_TOKENIZER_H_