Revert of Fix a crash that MediaPlayerAndroid weak_ptr is incorrectly used across thread

Revert of Fix a crash that MediaPlayerAndroid weak_ptr is incorrectly used across thread (patchset #1 id:1 of https://codereview.chromium.org/899473002/)

Reason for revert:
this CL doesn't fix the original issue

Original issue's description:
> Fix a crash that MediaPlayerAndroid weak_ptr is incorrectly used across thread
>
> For MediaPlayerListener, the callbacks can happen on a non-UI thread.
> Weak_ptr is not thread safe, so we shouldn't bind the weak_ptr in those callbacks.
> This change creates a threadsafe proxy class to bridge all the callbacks.
>
> BUG=453581, 447368, 447367
>
> Committed: https://crrev.com/2e9885788692f69203a98fb42347428ef553d640
> Cr-Commit-Position: refs/heads/master@{#314241}

TBR=xhwang@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=453581, 447368, 447367
Committed: https://crrev.com/aba6a96e10ca6593a7f97caf9f8f8bcf2894e0ee
Cr-Commit-Position: refs/heads/master@{#315352}

[qinmin, 2015-02-09 18:47:22]

Created Revert of Fix a crash that MediaPlayerAndroid weak_ptr is incorrectly
used across thread

[commit-bot: I haz the power, 2015-02-09 18:47:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/879273006/1

[commit-bot: I haz the power, 2015-02-09 18:49:07]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-09 18:50:54]

Patchset 1 (id:??) landed as
https://crrev.com/aba6a96e10ca6593a7f97caf9f8f8bcf2894e0ee
Cr-Commit-Position: refs/heads/master@{#315352}