Merge pull request #684 from yunxliu/yunxliu/webapi/mediaRenderer_update

[webapi] Update 44 TCs for MediaRenderer
[usecase-webapi] Improve w3c usecase FlexibleBox

- Add black top bar for flexibleBox page

Impacted tests(approved): new 0, update 1, delete 0
Unit test platform: [Tizen IVI][Android]
Unit test result summary: pass 1, fail 0, block 0