Avoid inline->fullscreen reload for html5 video.

Now when a user start inline play and then switch to full screen, there is no
reload any more.
Basically, we change mediaplayer as a static member, and detect possible
situation to skip the prepare work.

bug:5710646

Change-Id: Ida34cf2e919a6cc8e0d52cd1175d51b5f5d527f7