Fix a crash in the FileSystem API when the app window closes during a call.

chrome/browser/extensions/api/file_system/file_system_api.cc

 // Copyright (c) 2012 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/extensions/api/file_system/file_system_api.h"
 
 #include "apps/saved_files_service.h"
 #include "apps/shell_window.h"
 #include "apps/shell_window_registry.h"
 #include "base/bind.h"
@@ skipping 321 matching lines @@
       is_directory_,
       base::Bind(&FileSystemEntryFunction::RegisterFileSystemsAndSendResponse,
                  this,
                  paths),
       base::Bind(&FileSystemEntryFunction::HandleWritableFileError, this));
 }
 
 void FileSystemEntryFunction::RegisterFileSystemsAndSendResponse(
     const std::vector<base::FilePath>& paths) {
   DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
+  if (!render_view_host_)
+    return;
 
   CreateResponse();
   for (std::vector<base::FilePath>::const_iterator it = paths.begin();
        it != paths.end(); ++it) {
     AddEntryToResponse(*it, "");
   }
   SendResponse(true);
 }
 
 void FileSystemEntryFunction::CreateResponse() {
@@ skipping 653 matching lines @@
   if (needs_new_entry) {
     is_directory_ = file_entry->is_directory;
     CreateResponse();
     AddEntryToResponse(file_entry->path, file_entry->id);
   }
   SendResponse(true);
   return true;
 }
 
 }  // namespace extensions