Fix bug 880930 - JS debugger: RootActor needs its own definition of windowMediator. r=past

--HG--
extra : transplant_source : %DB%A6H%9B%D0%00%B4%24t%89%F0r%F9r%9C%7B%EC%07%D0%1B
Bug 902421 - Add correct paths to the SrcdirProvider. r=dcamp
Bug 911982 - Markup mutations are flashed in the markup-view; r=jwalker