[Android] Add test case for getUrl().

This patch is to add test case for getUrl().
Open a url, get the url on ui thread, compare it with the expected.
Merge pull request #1935 from wuhengzhi/getUrl_test

[Android] Add test case for getUrl().
[Android] Add test case for clearCache().

This patch is to add test case for clearCache().
Request the url from TestWebServer, record the hit count to
webserver and compare the count with the expected number.