Allow WebUI Tests to use preLoad in HtmlDialogUI.

chrome/test/data/webui/print_preview.cc

Index: chrome/test/data/webui/print_preview.cc
diff --git a/chrome/test/data/webui/print_preview.cc b/chrome/test/data/webui/print_preview.cc
new file mode 100644
index 0000000000000000000000000000000000000000..becc7639cd7f2381297398e380d9bb87f5d03610
--- /dev/null
+++ b/chrome/test/data/webui/print_preview.cc
@@ -0,0 +1,15 @@
+// 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/test/data/webui/print_preview.h"
+
+PrintPreviewWebUITest::PrintPreviewWebUITest() {}
+
+PrintPreviewWebUITest::~PrintPreviewWebUITest() {}
+
+// Always print preview for testing.
+void PrintPreviewWebUITest::SetUpCommandLine(CommandLine* command_line) {
+  WebUIBrowserTest::SetUpCommandLine(command_line);
+  command_line->AppendSwitch(switches::kEnablePrintPreview);
+}