Fix the validation of the keyframe requests.

Fix the validation of the key frame requests.

1. Initialize |next_keyframe_at_| to 0, so that the expected sequence will be i * |keyframe_period_|.
2. Update |next_keyframe_at_|, when a key frame is arrived at the requested window. Other key frames should be ignored.

BUG=470775
TEST=Run the binary on Samus and Peach-Pit

Committed: https://crrev.com/7ae211fe61dad3e0fc129db8667b1aa922f3fb7b
Cr-Commit-Position: refs/heads/master@{#326724}

[Owen Lin, 2015-04-22 07:19:35]

owenlin@chromium.org changed reviewers:
+ posciak@chromium.org, wuchengli@chromium.org

[Owen Lin, 2015-04-22 07:19:36]

PTAL.

[Pawel Osciak, 2015-04-22 08:22:13]

On 2015/04/22 07:19:36, Owen Lin wrote:
> PTAL.

This is unfortunately going back to the issues I fixed in
https://codereview.chromium.org/942693003. I will explain more in the bug.

[Owen Lin, 2015-04-23 06:30:48]

On 2015/04/22 08:22:13, Pawel Osciak wrote:
> On 2015/04/22 07:19:36, Owen Lin wrote:
> > PTAL.
> 
> This is unfortunately going back to the issues I fixed in
> https://codereview.chromium.org/942693003. I will explain more in the bug.

Indeed!! I changed it back. :p. 

I got your point and see why you update the |next_keyframe_at_| when getting a
key frame. I try to fix this issue by initialize the |next_keyframe_at_| to 0.
Since it is how we requested for key frames.

In addition, the |next_keyframe_| will only be updated when the key frame comes
in the correct window. I think this is the bug that why the test passed. On
peach-pit, the first two frames are key frames.

[Pawel Osciak, 2015-04-24 01:20:07]

lgtm, but please update the CL message

[Owen Lin, 2015-04-24 02:07:39]

On 2015/04/24 01:20:07, Pawel Osciak wrote:
> lgtm, but please update the CL message

Done. Thanks.

[Owen Lin, 2015-04-24 02:07:43]

The CQ bit was checked by owenlin@chromium.org

[commit-bot: I haz the power, 2015-04-24 02:07:53]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1056133009/20001

[commit-bot: I haz the power, 2015-04-24 02:35:37]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-04-24 02:37:33]

Patchset 2 (id:??) landed as
https://crrev.com/7ae211fe61dad3e0fc129db8667b1aa922f3fb7b
Cr-Commit-Position: refs/heads/master@{#326724}