Use FilterContext to allow filters to access URLRequestJob data...

net/url_request/url_request_file_job.cc

 // Copyright (c) 2006-2008 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.
 
 // For loading files, we make use of overlapped i/o to ensure that reading from
 // the filesystem (e.g., a network filesystem) does not block the calling
 // thread.  An alternative approach would be to use a background thread or pool
 // of threads, but it seems better to leverage the operating system's ability
 // to do background file reads for us.
 //
@@ skipping 132 matching lines @@
 
   // Otherwise, a read error occured.  We may just need to wait...
   if (rv == net::ERR_IO_PENDING) {
     SetStatus(URLRequestStatus(URLRequestStatus::IO_PENDING, 0));
   } else {
     NotifyDone(URLRequestStatus(URLRequestStatus::FAILED, rv));
   }
   return false;
 }
 
-bool URLRequestFileJob::GetMimeType(std::string* mime_type) {
+bool URLRequestFileJob::GetMimeType(std::string* mime_type) const {
   DCHECK(request_);
   return net::GetMimeTypeFromFile(file_path_, mime_type);
 }
 
 void URLRequestFileJob::DidResolve(
     bool exists, const file_util::FileInfo& file_info) {
 #if defined(OS_WIN)
   async_resolver_ = NULL;
 #endif
 
@@ skipping 55 matching lines @@
     return false;
 
   *location = net::FilePathToFileURL(new_path);
   *http_status_code = 301;
   return true;
 #else
   return false;
 #endif
 }