Remove legacy StartsWithASCII function.

tools/gn/filesystem_utils.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/filesystem_utils.h"
 
 #include <algorithm>
 
 #include "base/files/file_util.h"
 #include "base/logging.h"
@@ skipping 730 matching lines @@
   if (source_dir.is_source_absolute()) {
     // The source dir is source-absolute, so we trim off the two leading
     // slashes to append to the toolchain object directory.
     result.value().append(&source_dir.value()[2],
                           source_dir.value().size() - 2);
   } else {
     // System-absolute.
     const std::string& build_dir =
         settings->build_settings()->build_dir().value();
 
-    if (base::StartsWithASCII(source_dir.value(), build_dir, true)) {
+    if (base::StartsWith(source_dir.value(), build_dir,
+                         base::CompareCase::SENSITIVE)) {
       size_t build_dir_size = build_dir.size();
       result.value().append(&source_dir.value()[build_dir_size],
                             source_dir.value().size() - build_dir_size);
     } else {
       result.value().append("ABS_PATH");
 #if defined(OS_WIN)
       // Windows absolute path contains ':' after drive letter. Remove it to
       // avoid inserting ':' in the middle of path (eg. "ABS_PATH/C:/").
       std::string src_dir_value = source_dir.value();
       const auto colon_pos = src_dir_value.find(':');
@@ skipping 51 matching lines @@
 
 SourceDir GetCurrentOutputDir(const Scope* scope) {
   return GetOutputDirForSourceDirAsOutputFile(
       scope->settings(), scope->GetSourceDir()).AsSourceDir(
           scope->settings()->build_settings());
 }
 
 SourceDir GetCurrentGenDir(const Scope* scope) {
   return GetGenDirForSourceDir(scope->settings(), scope->GetSourceDir());
 }