Keep browser process alive while there are platform apps with background pages running.

chrome/browser/chromeos/extensions/external_filesystem_apitest.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 "base/bind.h"
 #include "base/file_path.h"
 #include "base/file_util.h"
 #include "base/json/json_file_value_serializer.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/message_loop_proxy.h"
@@ skipping 306 matching lines @@
       test_data_dir_.AppendASCII("filebrowser_component"));
   ASSERT_TRUE(extension) << message_;
   std::string path = "filesystem:chrome-extension://" + extension->id() +
       "/external" + test_file.value();
   GURL url = extension->GetResourceURL("intent.html#" + path);
   ui_test_utils::NavigateToURL(browser(), url);
 
   // The webintent_handler sends chrome.test.succeed() on successful receipt
   // of the incoming Web Intent.
   ASSERT_TRUE(catcher.GetNextResult()) << message_;
+  CloseShellWindowsAndWaitForAppToExit();
 }
 
 IN_PROC_BROWSER_TEST_F(FileSystemExtensionApiTest, FileBrowserTestWrite) {
   AddTmpMountPoint();
   ASSERT_TRUE(RunExtensionTest("filesystem_handler_write")) << message_;
   ASSERT_TRUE(RunExtensionSubtest(
       "filebrowser_component", "write.html", kComponentFlags)) << message_;
 }
 
 IN_PROC_BROWSER_TEST_F(FileSystemExtensionApiTest,
@@ skipping 100 matching lines @@
                            _, _))
       .WillOnce(MockDownloadFileCallback(google_apis::HTTP_SUCCESS));
 
   // On exit, all operations in progress should be cancelled.
   EXPECT_CALL(*mock_drive_service_, CancelAll());
 
   // All is set... RUN THE TEST.
   EXPECT_TRUE(RunExtensionSubtest("filebrowser_component", "remote_search.html",
       kComponentFlags)) << message_;
 }