Cast: Merge common functionality from audio/video sender into frame_sender.

Cast: Merge common functionality from audio/video sender into frame_sender.

To make things simpler, also make congestion control into an interface with
fixed and adaptive implementations.

BUG=405622
Committed: https://crrev.com/47581b1fd39e86c350d90a843b510e9f6b79003e
Cr-Commit-Position: refs/heads/master@{#293630}

[hubbe, 2014-09-05 06:45:38]

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

[Alpha Left Google, 2014-09-05 19:40:59]

The CQ bit was checked by hclam@chromium.org

[Alpha Left Google, 2014-09-05 19:41:00]

lgtm

[commit-bot: I haz the power, 2014-09-05 19:42:15]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/hubbe@chromium.org/542883004/1

[commit-bot: I haz the power, 2014-09-05 20:46:33]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-09-05 20:46:34]

Failed to commit the patch.

[hubbe, 2014-09-05 21:11:09]

The CQ bit was checked by hubbe@chromium.org

[commit-bot: I haz the power, 2014-09-05 21:12:37]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/hubbe@chromium.org/542883004/20001

[commit-bot: I haz the power, 2014-09-06 03:14:02]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-09-06 03:14:04]

Exceeded time limit waiting for builds to trigger.

[hubbe, 2014-09-06 19:44:47]

The CQ bit was checked by hubbe@chromium.org

[commit-bot: I haz the power, 2014-09-06 19:45:31]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/hubbe@chromium.org/542883004/20001

[commit-bot: I haz the power, 2014-09-06 19:46:31]

Committed patchset #2 (id:20001) as 4ae3edf11a6fe7352719a349e9e93b724c319526

[commit-bot: I haz the power, 2014-09-10 03:43:11]

Patchset 2 (id:??) landed as
https://crrev.com/47581b1fd39e86c350d90a843b510e9f6b79003e
Cr-Commit-Position: refs/heads/master@{#293630}