GN: Add logging for the location of an invocation.

tools/gn/tokenizer.cc

 // 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.
 
 #include "tools/gn/tokenizer.h"
 
 #include "base/logging.h"
 #include "tools/gn/input_file.h"
 
 namespace {
@@ skipping 46 matching lines @@
   if (value == "<")
     return Token::LESS_THAN;
   if (value == ">")
     return Token::GREATER_THAN;
   if (value == "&&")
     return Token::BOOLEAN_AND;
   if (value == "||")
     return Token::BOOLEAN_OR;
   if (value == "!")
     return Token::BANG;
-  NOTREACHED();
   return Token::INVALID;
 }
 
 }  // namespace
 
 Tokenizer::Tokenizer(const InputFile* input_file, Err* err)
     : input_file_(input_file),
       input_(input_file->contents()),
       err_(err),
       cur_(0),
@@ skipping 279 matching lines @@
   } else if (cur_char() == '/' && cur_ + 1 < input_.size() &&
       (input_[cur_ + 1] == '/' || input_[cur_ + 1] == '*')) {
     // Different types of comments.
     help = "Comments should start with # instead";
   } else {
     help = "I have no idea what this is.";
   }
 
   return Err(location, "Invalid token.", help);
 }