Enable a11y audit for chrome://print and fix failing tests.

chrome/test/data/webui/print_preview.h

 // 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.
 
 #ifndef CHROME_TEST_DATA_WEBUI_PRINT_PREVIEW_H_
 #define CHROME_TEST_DATA_WEBUI_PRINT_PREVIEW_H_
 
 #include "chrome/test/base/web_ui_browser_test.h"
 
 class PrintPreviewWebUITest : public WebUIBrowserTest {
  public:
   PrintPreviewWebUITest();
   virtual ~PrintPreviewWebUITest();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(PrintPreviewWebUITest);
 };
 
+class PrintPreviewWebUIAsyncTest : public PrintPreviewWebUITest {

[Dan Beam, 2014/10/20 20:15:25]

why can't we do the inheritance in JS only?

[hcarmona, 2014/10/21 01:07:17]

Don't know, but I was getting compile errors in the unit test without the change
here. I will look into it.

+ public:
+  PrintPreviewWebUIAsyncTest();
+  virtual ~PrintPreviewWebUIAsyncTest();
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(PrintPreviewWebUIAsyncTest);
+};
+
 #endif  // CHROME_TEST_DATA_WEBUI_PRINT_PREVIEW_H_