[Android] Add test case for size(), hasItemAt() and getItemAt().

This patch is to add test case for size(), hasItemAt() and getItemAt().
Load url and get history size, get item at specified index, compare them with the expected result.
Judge whether has item at specified index.
`getItemAtOnUiThread(-1)` will return null and not throw an exception, see https://github.com/crosswalk-project/crosswalk/blob/master/runtime/android/core/src/org/xwalk/core/XWalkNavigationHistory.java#L51. 
I don't quite understanding the `fail()` here. I assume you think `getItemAtOnUiThread(-1)` will throw an exception, so you catch it, and if it does not, treat it as failure and call `fail()`.

But that's not true, I think here just
```
assertTrue(getItemAtOnUiThread(-1)==null);
```
is ok.