MediaPlayer cleanup, part one of N

MediaPlayer cleanup, part one of N

Get rid of a lot of dead code in MediaPlayer and associated classes,
and simplify MediaPlayer now that there's only a single MediaEngine
to worry about.

Note that this is just the beginning: there's clearly lots more to be
done, and some the layers here probably no longer need to exist.

R=eseidel@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=149779

[eseidel, 2013-05-04 01:14:52]

lgtm

We should figure out who wants to own the media code.  It was sherkus? I think
long ago.

I'm not your best reviewer, but this looks fine.  Sorry for the slow review.

[commit-bot: I haz the power, 2013-05-04 01:15:06]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/adamk@chromium.org/14722011/1

[commit-bot: I haz the power, 2013-05-04 03:27:15]

Retried try job too often on linux_layout_rel for step(s) webkit_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_layo...

[commit-bot: I haz the power, 2013-05-05 17:17:52]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/adamk@chromium.org/14722011/1

[commit-bot: I haz the power, 2013-05-05 17:47:58]

Retried try job too often on linux_layout_rel for step(s) webkit_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_layo...

[commit-bot: I haz the power, 2013-05-06 18:50:16]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/adamk@chromium.org/14722011/1

[commit-bot: I haz the power, 2013-05-06 19:36:23]

Change committed as 149779