The WebMediaPlayerCast class is-a RendererMediaPlayerInterface, which
has methods that look like blink::WebMediaPlayer methods, but it is
a chromium-style class. The WebMediaPlayerAndroid is-a
blink::WebMediaPlayer and also a RendererMediaPlayerInterface so
its overrides end up overriding both at once. This is problematic
because, while also being difficult to follow where control flow
goes, when the blink names are renamed in the Great Blink Rename to
be chromium style, incorrectly-blink-styled names outside of blink
will not be renamed and the inheritance here will break.

The two methods here are hasVideo() and paused(). It turns out that
neither method is ever used as part of the
RendererMediaPlayerInterface. And only paused() is used as part of
the concrete WebMediaPlayerCast class. So I have removed them both
from the RendererMediaPlayerInterface and added IsPaused() as a
non-virtual method on WebMediaPlayerCast instead.

R=hubbe@chromium.org
BUG=578344

Review-Url: https://codereview.chromium.org/2619593002
Cr-Commit-Position: refs/heads/master@{#442052}