[Android] Add the test case for addJavascriptInterface.

In this test case, we should use "@JavascriptInterface", it's from
"org.xwalk.core.JavascriptInterface", not
"android.webkit.JavascriptInterface".
In addition, if the target sdk version will be equal to or greater
than 17, "@JvascriptInterface" is required.

BUG=XWALK-1595
Merge pull request #1875 from wuhengzhi/addJavascriptInterface

[Android] Add the test case for addJavascriptInterface.