Revert of Pass initDataType instead of contentType on OnNeedKey().

Revert of Pass initDataType instead of contentType on OnNeedKey(). (patchset #4 id:60001 of https://codereview.chromium.org/611513005/)

Reason for revert:
This broke media/encrypted-media/encrypted-media-needkey.html on Linux (at least)

Original issue's description:
> Pass initDataType instead of contentType to OnNeedKey().
>
> BUG=224786
>
> Committed: https://crrev.com/2983dc91cc0bc7be6014f4bfc5cb19cc6e262a0b
> Cr-Commit-Position: refs/heads/master@{#297523}

TBR=ddorwin@chromium.org,sandersd@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=224786
Committed: https://crrev.com/de394fa4553674e0aa522ce7c3483394f0f40d3d
Cr-Commit-Position: refs/heads/master@{#297538}

[Zhenyao Mo, 2014-09-30 23:18:24]

Created Revert of Pass initDataType instead of contentType on OnNeedKey().

[commit-bot: I haz the power, 2014-09-30 23:19:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/616183002/1

[commit-bot: I haz the power, 2014-09-30 23:20:37]

Committed patchset #1 (id:1) as 04cf114236e2d75331784ce85b8e250b8017e2cb

[commit-bot: I haz the power, 2014-09-30 23:21:19]

Patchset 1 (id:??) landed as
https://crrev.com/de394fa4553674e0aa522ce7c3483394f0f40d3d
Cr-Commit-Position: refs/heads/master@{#297538}