Revert 175683 "Eliminate MediaPlayer & MediaPlayerClient abstrac..."

> Eliminate MediaPlayer & MediaPlayerClient abstractions(rate, setRate and other APIs)
> 
> BUG=350571
> 
> Chromium side patch for this is https://codereview.chromium.org/303403002/
> 
> Review URL: https://codereview.chromium.org/304353005

TBR=srirama.m@samsung.com

Review URL: https://codereview.chromium.org/320053003

git-svn-id: svn://svn.chromium.org/blink/trunk@175711 bbb929c8-8fbe-4397-9dbb-9b2b20218538