[url] Reserve size in a smarter way to account for pre-allocated buffers

url/url_canon_relative.cc

 // Copyright 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.
 
 // Canonicalizer functions for working with and resolving relative URLs.
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "url/url_canon.h"
@@ skipping 270 matching lines @@
   // We know the authority section didn't change, copy it to the output. We
   // also know we have a path so can copy up to there.
   Component path, query, ref;
   ParsePathInternal(relative_url, relative_component, &path, &query, &ref);
 
   // Canonical URLs always have a path, so we can use that offset. Reserve
   // enough room for the base URL, the new path, and some extra bytes for
   // possible escaped characters.
   output->ReserveSizeIfNeeded(
       base_parsed.path.begin +
-      std::max(path.end(), std::max(query.end(), ref.end())) + 8);
+      std::max(path.end(), std::max(query.end(), ref.end())));
   output->Append(base_url, base_parsed.path.begin);
 
   if (path.len > 0) {
     // The path is replaced or modified.
     int true_path_begin = output->length();
 
     // For file: URLs on Windows, we don't want to treat the drive letter and
     // colon as part of the path for relative file resolution when the
     // incoming URL does not provide a drive spec. We save the true path
     // beginning so we can fix it up after we are done.
@@ skipping 97 matching lines @@
   replacements.SetHost(relative_url, relative_parsed.host);
   replacements.SetPort(relative_url, relative_parsed.port);
   replacements.SetPath(relative_url, relative_parsed.path);
   replacements.SetQuery(relative_url, relative_parsed.query);
   replacements.SetRef(relative_url, relative_parsed.ref);
 
   // Length() does not include the old scheme, so make sure to add it from the
   // base URL.
   output->ReserveSizeIfNeeded(
       replacements.components().Length() +
-      base_parsed.CountCharactersBefore(Parsed::USERNAME, false) + 8);
+      base_parsed.CountCharactersBefore(Parsed::USERNAME, false));
   return ReplaceStandardURL(base_url, base_parsed, replacements,
                             query_converter, output, out_parsed);
 }
 
 // Resolves a relative URL that happens to be an absolute file path. Examples
 // include: "//hostname/path", "/c:/foo", and "//hostname/c:/foo".
 template<typename CHAR>
 bool DoResolveAbsoluteFile(const CHAR* relative_url,
                            const Component& relative_component,
                            CharsetConverter* query_converter,
@@ skipping 148 matching lines @@
                         const Component& relative_component,
                         CharsetConverter* query_converter,
                         CanonOutput* output,
                         Parsed* out_parsed) {
   return DoResolveRelativeURL<base::char16>(
       base_url, base_parsed, base_is_file, relative_url,
       relative_component, query_converter, output, out_parsed);
 }
 
 }  // namespace url