media: Move CdmInitializedPromise to media/.

media: Move CdmInitializedPromise to media/.

This class does not need to be in content/ and will be needed by MojoCdm in
media/mojo.

BUG=432998
TEST=Moves file only.

Committed: https://crrev.com/fa492ce90438a9ab2aaa21acd467525bf27e8801
Cr-Commit-Position: refs/heads/master@{#334266}

[xhwang, 2015-06-12 22:05:50]

xhwang@chromium.org changed reviewers:
+ jrummell@chromium.org

[xhwang, 2015-06-12 22:05:51]

xhwang@chromium.org changed reviewers:
+ jrummell@chromium.org

[xhwang, 2015-06-12 22:05:52]

PTAL

[xhwang, 2015-06-12 22:05:52]

PTAL

[xhwang, 2015-06-12 22:06:35]

jrummell: PTAL
ddorwin: FYI

[jrummell, 2015-06-12 22:17:16]

lgtm

[xhwang, 2015-06-12 22:25:23]

The CQ bit was checked by xhwang@chromium.org

[commit-bot: I haz the power, 2015-06-12 22:26:03]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1187603003/1

[commit-bot: I haz the power, 2015-06-12 22:56:34]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-12 22:57:27]

Patchset 1 (id:??) landed as
https://crrev.com/fa492ce90438a9ab2aaa21acd467525bf27e8801
Cr-Commit-Position: refs/heads/master@{#334266}