Use ExternalFileSystemBackend in the DriveURLRequestJob.

chrome/browser/chromeos/fileapi/file_system_backend.cc

 // Copyright 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 "chrome/browser/chromeos/fileapi/file_system_backend.h"
 
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/strings/stringprintf.h"
 #include "chrome/browser/chromeos/fileapi/file_access_permissions.h"
 #include "chrome/browser/chromeos/fileapi/file_system_backend_delegate.h"
 #include "chrome/browser/media_galleries/fileapi/media_file_system_backend.h"
+#include "chrome/common/url_constants.h"
 #include "chromeos/dbus/cros_disks_client.h"
 #include "storage/browser/blob/file_stream_reader.h"
 #include "storage/browser/fileapi/async_file_util.h"
 #include "storage/browser/fileapi/external_mount_points.h"
 #include "storage/browser/fileapi/file_stream_writer.h"
 #include "storage/browser/fileapi/file_system_context.h"
 #include "storage/browser/fileapi/file_system_operation.h"
 #include "storage/browser/fileapi/file_system_operation_context.h"
 #include "storage/browser/fileapi/file_system_url.h"
 
@@ skipping 150 matching lines @@
     return false;
 
   std::string extension_id = url.origin().host();
   // TODO(mtomasz): Temporarily whitelist TimeScapes. Remove this in M-31.
   // See: crbug.com/271946
   if (extension_id == "mlbmkoenclnokonejhlfakkeabdlmpek" &&
       url.type() == storage::kFileSystemTypeRestrictedNativeLocal) {
     return true;
   }
 
+  if (url.origin().scheme() == chrome::kDriveScheme)

[mtomasz, 2014/09/19 05:30:53]

nit: We should either have a test that such url can't be passed from an
extension, or at least a comment why it's safe.

[hirono, 2014/09/19 06:26:36]

I added a comment. Let me add a test to prohibit parsing
filesystem:externalfile:/xxx, in the future CL. I'm planning to add it to
external_file_url_util.cc.
https://codereview.chromium.org/580023003/patch/20001/30017

+    return true;
+
   // Check first to make sure this extension has fileBrowserHander permissions.
   if (!special_storage_policy_.get() ||
       !special_storage_policy_->IsFileHandler(extension_id))
     return false;
 
   return file_access_permissions_->HasAccessPermission(extension_id,
                                                        url.virtual_path());
 }
 
 void FileSystemBackend::GrantFullAccessToExtension(
@@ skipping 233 matching lines @@
     case storage::kFileSystemTypeRestrictedNativeLocal:
       callback.Run(GURL());
       return;
     default:
       NOTREACHED();
   }
   callback.Run(GURL());
 }
 
 }  // namespace chromeos