Support unprefixed EME in HTMLViewer.

Support unprefixed EME in HTMLViewer.

Tested with:
out/GN/mojo_shell
http://<host>/LayoutTests/media/encrypted-media/encrypted-media-playback-setmediakeys-before-src.html
--args-for='mojo://html_viewer --v=3 --enable-encrypted-media'

TBR=jamesr@chromium.org
BUG=444205
TEST=See above.

Committed: https://crrev.com/f549b3d45ef6c93c41e101d1d0dbeebffbad7222
Cr-Commit-Position: refs/heads/master@{#309565}

[xhwang, 2014-12-20 00:16:03]

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

[xhwang, 2014-12-20 00:16:04]

jrummell: Please review from EME's perspective.
jamesr: Please review from HTMLViewer's perspective.

ddorwin: FYI

[xhwang, 2014-12-22 18:06:09]

rebase only

[jrummell, 2014-12-23 01:01:04]

lgtm.

[xhwang, 2014-12-23 17:51:53]

TBRing jamesr...

[xhwang, 2014-12-23 17:54:38]

The CQ bit was checked by xhwang@chromium.org

[commit-bot: I haz the power, 2014-12-23 17:55:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/815293002/20001

[commit-bot: I haz the power, 2014-12-23 18:44:33]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2014-12-23 18:45:30]

Patchset 2 (id:??) landed as
https://crrev.com/f549b3d45ef6c93c41e101d1d0dbeebffbad7222
Cr-Commit-Position: refs/heads/master@{#309565}