[Android] Implement onShowCustomView with requested orientation.

This patch is to implement the onShowCustomView function with requested
orientation.

BUG=XWALK-1868
[Android] Add test case for onShow/HideCustomView.

This patch is to add test for OnShowCustomView and onHideCustomView.
Some code was ported from android webview.
Merge pull request #2598 from wuhengzhi/show_custom_view_impl

[Android] Implement onShowCustomView and add test case.