Move ReadFileToString to the base namespace.

tools/gn/function_read_file.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 "base/file_util.h"
 #include "tools/gn/err.h"
 #include "tools/gn/filesystem_utils.h"
 #include "tools/gn/functions.h"
 #include "tools/gn/input_conversion.h"
 #include "tools/gn/input_file.h"
@@ skipping 42 matching lines @@
   const SourceDir& cur_dir = scope->GetSourceDir();
   SourceFile source_file = cur_dir.ResolveRelativeFile(args[0].string_value());
   base::FilePath file_path =
       scope->settings()->build_settings()->GetFullPath(source_file);
 
   // Ensure that everything is recomputed if the read file changes.
   g_scheduler->AddGenDependency(file_path);
 
   // Read contents.
   std::string file_contents;
-  if (!file_util::ReadFileToString(file_path, &file_contents)) {
+  if (!base::ReadFileToString(file_path, &file_contents)) {
     *err = Err(args[0], "Could not read file.",
                "I resolved this to \"" + FilePathToUTF8(file_path) + "\".");
     return Value();
   }
 
   return ConvertInputToValue(file_contents, function, args[1], err);
 }
 
 }  // namespace functions