Make GN build work on Mac again.

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/file_util.h"
 #include "base/logging.h"
@@ skipping 161 matching lines @@
   if (extension == "h")
     return SOURCE_H;
   if (extension == "c")
     return SOURCE_C;
   if (extension == "m")
     return SOURCE_M;
   if (extension == "mm")
     return SOURCE_MM;
   if (extension == "rc")
     return SOURCE_RC;
-  if (extension == "S")
+  if (extension == "S" || extension == "s")
     return SOURCE_S;
 
   return SOURCE_UNKNOWN;
 }
 
 const char* GetExtensionForOutputType(Target::OutputType type,
                                       Settings::TargetOS os) {
   switch (os) {
     case Settings::MAC:
       switch (type) {
@@ skipping 515 matching lines @@
   return GetGenDirForSourceDir(target->settings(), target->label().dir());
 }
 
 SourceDir GetCurrentOutputDir(const Scope* scope) {
   return GetOutputDirForSourceDir(scope->settings(), scope->GetSourceDir());
 }
 
 SourceDir GetCurrentGenDir(const Scope* scope) {
   return GetGenDirForSourceDir(scope->settings(), scope->GetSourceDir());
 }