Replace base::str[n]casecmp with helper functions.

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 65 matching lines @@
 }
 
 // Attempts to do a case and slash-insensitive comparison of two 8-bit Windows
 // paths.
 bool AreAbsoluteWindowsPathsEqual(const base::StringPiece& a,
                                   const base::StringPiece& b) {
   if (a.size() != b.size())
     return false;
 
   // For now, just do a case-insensitive ASCII comparison. We could convert to
-  // UTF-16 and use ICU if necessary. Or maybe base::strcasecmp is good enough?
+  // UTF-16 and use ICU if necessary.
   for (size_t i = 0; i < a.size(); i++) {
     if (NormalizeWindowsPathChar(a[i]) != NormalizeWindowsPathChar(b[i]))
       return false;
   }
   return true;
 }
 
 bool DoesBeginWindowsDriveLetter(const base::StringPiece& path) {
   if (path.size() < 3)
     return false;
@@ skipping 716 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());
 }