[Windows] Enable aura on Windows

The origin MACRO protection for XWalkViewsDelegate
is "#if !defined(OS_WIN) && defined(USE_AURA)", which
is not appropriate on Windows after Windows build also
switches to use aura.

Change the condition to "#if defined(USE_AURA)" and
implement the missing abstract function on Windows.
[Windows] Fix runtime is using wrong content_app target

On Windows, upstream is trying to provide alternative to split
chrome.dll into several parts. Therefore, target content_app
is now content_app_browser, content_app_child, content_app_both.
It's not relevant with xwalk, xwalk should use content_app_both
to obtain all it need for content app.