RELAND: [Cast] Software encoder support for varying video frame sizes.

RELAND: [Cast] Software encoder support for varying video frame sizes.

Adds support for automatic on-line reconfiguration of the VP8 software
encoder whenever the video frame size changes.  libvpx supports
shrinking frame sizes without tearing down the encoder, but growing
frames sizes still requires a full tear-down and re-creation.

Most of this change involves adding extensive unit testing to confirm
media/cast is now capable of handling variable frames sizes end-to-end.
In addition, the cast_sender_app and cast_receiver_app diagnostic tools
have been updated.

An upcoming change will eliminate the width and height properties from
media::cast::VideoSenderConfig, which are both being ignored now.

BUG=451277
TBR=hubbe@chromium.org

Committed: https://crrev.com/9a739084bdf85aba9716205e2185ffb0a278d187
Cr-Commit-Position: refs/heads/master@{#314281}

[miu, 2015-02-03 04:38:07]

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

[miu, 2015-02-03 04:39:21]

hubbe: PTAL (a small oversight caused MSAN failures for the 3-buffer mode
tests).

[miu, 2015-02-03 04:39:37]

The CQ bit was checked by miu@chromium.org

[commit-bot: I haz the power, 2015-02-03 04:40:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/892383002/20001

[commit-bot: I haz the power, 2015-02-03 07:05:47]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-02-03 07:06:35]

Patchset 2 (id:??) landed as
https://crrev.com/9a739084bdf85aba9716205e2185ffb0a278d187
Cr-Commit-Position: refs/heads/master@{#314281}