[Android] Enable the feature for onRequestFocus.

This patch is to enable the feature for onRequestFocus().
Call onRequestFocus() in activateContents().
[Android] Add test case for onRequestFocus.

This patch is to add test case for OnRequestFocus().
Merge pull request #2323 from wuhengzhi/onRequestFocus_test

[Android] Enable the feature and add test case for onRequestFocus.