Remove HTMLMediaElement::togglePlayState()

It is unused.

BUG=none

Review URL: https://codereview.chromium.org/139233008

git-svn-id: svn://svn.chromium.org/blink/trunk@166758 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove MediaController::m_mediaGroup

It is unused.

BUG=none

Review URL: https://codereview.chromium.org/150423006

git-svn-id: svn://svn.chromium.org/blink/trunk@166759 bbb929c8-8fbe-4397-9dbb-9b2b20218538