Revert of Added stub MediaSourcePlayer for developing behind the flag

Revert of Added stub MediaSourcePlayer for developing behind the flag (patchset #13 id:240001 of https://codereview.chromium.org/1076013002/)

Reason for revert:
Broke Android Clang Builder (dbg):

http://build.chromium.org/p/chromium.linux/buildstatus?builder=Android%20Clang%20Builder%20%28dbg%29&number=59307

Original issue's description:
> Added stub MediaSourcePlayer for developing behind the flag
>
> Added a new experimental flag and stub implementation for
> the player. Created Media thread and redirected demuxer
> messages to it.
>
> BUG=none
>
> Committed: https://crrev.com/8ad68b12db7db320a37e39e94be8d45205fee626
> Cr-Commit-Position: refs/heads/master@{#329059}

TBR=qinmin@chromium.org,timav@google.com,xhwang@chromium.org,sievers@chromium.org,timav@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=none

Committed: https://crrev.com/9160c54f557035f966bed567e1bb7950d1479162
Cr-Commit-Position: refs/heads/master@{#329061}

[miu, 2015-05-10 01:37:33]

Created Revert of Added stub MediaSourcePlayer for developing behind the flag

[commit-bot: I haz the power, 2015-05-10 01:37:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1132973002/1

[commit-bot: I haz the power, 2015-05-10 01:40:05]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-10 01:41:04]

Patchset 1 (id:??) landed as
https://crrev.com/9160c54f557035f966bed567e1bb7950d1479162
Cr-Commit-Position: refs/heads/master@{#329061}