[Cast] Fix referenced_frame_ids emitted by Vp8Encoder, with massive test clean-up.

[Cast] Fix referenced_frame_ids emitted by Vp8Encoder, with massive test clean-up.

The referenced_frame_ids set by Vp8Encoder were wrong in two ways:
1) A recent change introduced an off-by-one error.  2) Math was being
done with results stored in a uint8 variable, which was causing the
upper 24 bits to be stripped.

Added VideoEncoderImplTest.GeneratesKeyFrameThenOnlyDeltaFrames test to
prevent future regressions.  In addition, a lot of unit test code clean-up
was done to beef-up existing testing while also removing useless tests.

Committed: https://crrev.com/738b28e4720cf936825deaf4303fdb085c9e0be4
Cr-Commit-Position: refs/heads/master@{#295493}

[miu, 2014-09-18 02:12:35]

miu@chromium.org changed reviewers:
+ hubbe@chromium.org

[miu, 2014-09-18 02:12:36]

hubbe: PTAL.  Fixed as discussed earlier today, with testing to prevent future
breakage.

[hubbe, 2014-09-18 17:28:07]

The CQ bit was checked by hubbe@chromium.org

[hubbe, 2014-09-18 17:28:07]

lgtm

[commit-bot: I haz the power, 2014-09-18 17:29:06]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/581903002/1

[commit-bot: I haz the power, 2014-09-18 17:55:27]

Committed patchset #1 (id:1) as 020596749116bcb69491bedafdb9f5eef72edc08

[commit-bot: I haz the power, 2014-09-18 17:56:33]

Patchset 1 (id:??) landed as
https://crrev.com/738b28e4720cf936825deaf4303fdb085c9e0be4
Cr-Commit-Position: refs/heads/master@{#295493}