gn: fix fuzzer bug in parser for stack local

tools/gn/parser.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/parser.h"
 
 #include <utility>
 
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
@@ skipping 806 matching lines @@
   std::vector<const ParseNode*> post;
   TraverseOrder(file, &pre, &post);
 
   // Assign line comments to syntax immediately following.
   int cur_comment = 0;
   for (auto* node : pre) {
     if (node->GetRange().is_null()) {
       CHECK_EQ(node, file) << "Only expected on top file node";
       continue;
     }
-    const Location& start = node->GetRange().begin();
+    const Location start = node->GetRange().begin();
     while (cur_comment < static_cast<int>(line_comment_tokens_.size())) {
       if (start.byte() >= line_comment_tokens_[cur_comment].location().byte()) {
         const_cast<ParseNode*>(node)->comments_mutable()->append_before(
             line_comment_tokens_[cur_comment]);
         ++cur_comment;
       } else {
         break;
       }
     }
   }
@@ skipping 35 matching lines @@
         break;
       }
     }
 
     // Suffix comments were assigned in reverse, so if there were multiple on
     // the same node, they need to be reversed.
     if ((*i)->comments() && !(*i)->comments()->suffix().empty())
       const_cast<ParseNode*>(*i)->comments_mutable()->ReverseSuffix();
   }
 }