This is UI side unreadable device support.

chrome/browser/chromeos/extensions/file_browser_event_router.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 "chrome/browser/chromeos/extensions/file_browser_event_router.h"
 
 #include "base/bind.h"
 #include "base/json/json_writer.h"
 #include "base/memory/singleton.h"
 #include "base/message_loop.h"
@@ skipping 314 matching lines @@
             FileManagerUtil::GetFileBrowserExtensionUrl().GetOrigin(),
             &source_url)) {
       mount_info_value->SetString("sourceUrl", source_url.spec());
     }
   } else {
     mount_info_value->SetString("sourceUrl", mount_info.source_path);
   }
 
   FilePath relative_mount_path;
   bool relative_mount_path_set = false;
-  // If there were no error, add mountPath to the event.
-  if (error_code == chromeos::MOUNT_ERROR_NONE) {
+
+  // If there were no error or some special conditions occured, add mountPath
+  // to the event.
+  if (error_code == chromeos::MOUNT_ERROR_NONE ||
+      !mount_info.special_data.empty()) {
     // Convert mount point path to relative path with the external file system
     // exposed within File API.
     if (FileManagerUtil::ConvertFileToRelativeFileSystemPath(profile_,
             FilePath(mount_info.mount_path),
             &relative_mount_path)) {
       mount_info_value->SetString("mountPath",
                                   "/" + relative_mount_path.value());
       relative_mount_path_set = true;
     }
   }
 
   std::string args_json;
   base::JSONWriter::Write(&args, false /* pretty_print */, &args_json);
   profile_->GetExtensionEventRouter()->DispatchEventToRenderers(
       extension_event_names::kOnFileBrowserMountCompleted, args_json, NULL,
       GURL());
 
   if (relative_mount_path_set &&
       mount_info.mount_type == chromeos::MOUNT_TYPE_DEVICE &&
+      mount_info.special_data != "unreadable_unknown_filesystem" &&
+      mount_info.special_data != "unreadable_unsupported_filesystem" &&
       event == chromeos::MountLibrary::MOUNTING) {
     FileManagerUtil::ShowFullTabUrl(profile_, FilePath(mount_info.mount_path));
   }
 }
 
 void ExtensionFileBrowserEventRouter::OnDiskAdded(
     const chromeos::MountLibrary::Disk* disk) {
   VLOG(1) << "Disk added: " << disk->device_path();
   if (disk->device_path().empty()) {
     VLOG(1) << "Empty system path for " << disk->device_path();
@@ skipping 158 matching lines @@
           &FileWatcherDelegate::HandleFileWatchOnUIThread,
           local_path,
           true));     // got_error
 }
 
 void
 ExtensionFileBrowserEventRouter::FileWatcherDelegate::HandleFileWatchOnUIThread(
      const FilePath& local_path, bool got_error) {
   router_->HandleFileWatchNotification(local_path, got_error);
 }