[Android] Fix three failed test cases in core test.

This patch is to fix three failed test cases about full screen, request
focus and file chooser.
This issue was caused by CL:https://codereview.chromium.org/518633002/
Fix it by loading javascript url, it will fake UserGestureIndicator from
WebLocalFrameImpl.

BUG=XWALK-2755
Merge pull request #2546 from wuhengzhi/fullscreen_requestfocus_filechooser_fail

[Android] Fix three failed test cases in core test.