Support low latency mode decoding in the H/W video decoder on Windows.

Support low latency mode decoding in the H/W video decoder on Windows.

This is enabled via an attribute CODECAPI_AVLowLatencyMode set on the decoder transform.
From testing I could see a reduction in the number of input packets before the first output frame was delivered
by the decoder. On vimeo, with this attribute, the first output frame came after 9-10 input packets. Without it
after 25-30 input packets. On the HTML5 quirksmode site, with this attribute the first output frame came after 9-11 input
packets. Without it it came after 16-17 input packets.

We can enable this on Canary to see how this fares in the wild.

BUG=456359
Committed: https://crrev.com/6e74dc46d6f01a95661a74be30465ef7978bfb80
Cr-Commit-Position: refs/heads/master@{#315151}

[ananta, 2015-02-06 23:35:55]

ananta@chromium.org changed reviewers:
+ dalecurtis@chromium.org

[DaleCurtis, 2015-02-06 23:39:24]

lgtm

[ananta, 2015-02-06 23:44:12]

The CQ bit was checked by ananta@chromium.org

[ananta, 2015-02-06 23:44:12]

The CQ bit was unchecked by ananta@chromium.org

[ananta, 2015-02-06 23:50:30]

The CQ bit was checked by ananta@chromium.org

[commit-bot: I haz the power, 2015-02-06 23:51:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/890603004/1

[commit-bot: I haz the power, 2015-02-07 00:51:51]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-07 00:52:20]

Patchset 1 (id:??) landed as
https://crrev.com/6e74dc46d6f01a95661a74be30465ef7978bfb80
Cr-Commit-Position: refs/heads/master@{#315151}