Add support for loading pak files from arbitrary file regions.

base/files/file.cc

 // Copyright (c) 2011 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/files/file.h"
 #include "base/files/file_path.h"
 
 namespace base {
 
 File::Info::Info()
     : size(0),
       is_directory(false),
       is_symbolic_link(false) {
 }
 
 File::Info::~Info() {
 }
 
+File::Region::Region(int64 offset, int64 size) : offset(offset), size(size) {
+  DCHECK_GE(offset, 0);
+}
+
+File::Region::Region(File& file) : offset(0), size(file.GetLength()) {
+  DCHECK_GE(size, 0);
+}
+
+File::Region::~Region() {
+}
+
 File::File()
     : error_details_(FILE_ERROR_FAILED),
       created_(false),
       async_(false) {
 }
 
 #if !defined(OS_NACL)
 File::File(const FilePath& name, uint32 flags)
     : error_details_(FILE_OK),
       created_(false),
@@ skipping 89 matching lines @@
       return "FILE_ERROR_IO";
     case FILE_ERROR_MAX:
       break;
   }
 
   NOTREACHED();
   return "";
 }
 
 }  // namespace base