Clean-up: Remove accelerated subscriber switch for tab/desktop capture.

Clean-up: Remove accelerated subscriber switch for tab/desktop capture.

Removes a compile-time switch and associated logic that was necessary in
the pre-Aura days where content change signals were not reliable.

Committed: https://crrev.com/67cc124f207b423ab020b44a91bc4a72f9dec32b
Cr-Commit-Position: refs/heads/master@{#318594}

[miu, 2015-02-27 01:49:58]

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

[miu, 2015-02-27 01:49:59]

hubbe: PTAL at long-time wanting TODO.

[hubbe, 2015-02-28 00:34:04]

lgtm

[miu, 2015-02-28 03:11:35]

The CQ bit was checked by miu@chromium.org

[commit-bot: I haz the power, 2015-02-28 03:12:24]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/962503005/1

[commit-bot: I haz the power, 2015-02-28 04:46:11]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-28 04:46:49]

Patchset 1 (id:??) landed as
https://crrev.com/67cc124f207b423ab020b44a91bc4a72f9dec32b
Cr-Commit-Position: refs/heads/master@{#318594}