Tests for the window's length attribute
Update pull request #693

1. Add tests to check the child browsing context by frame, object and embed elements
2. Rename files and etc

Signed-off-by: xiaojunwu <xiaojunx.a.wu@intel.com>
Update test2.html as review suggestions
Remvoe an unuseful assertion
Update according to review comments
Update an assertion
Merge pull request #693 from xiaojunwu/submission/xiaojunwu/window-length

Tests for the window's length attribute