Revert of De-dupe copy requests for tab capture in DelegatedFrameHost.

Revert of De-dupe copy requests for tab capture in DelegatedFrameHost. (patchset #7 id:160001 of https://codereview.chromium.org/986823002/)

Reason for revert:
Weird frame flickering effect in capture on some systems.  https://crbug.com/469345

Original issue's description:
> De-dupe copy requests for tab capture in DelegatedFrameHost.
>
> Tab capture requests copies/readbacks in response to every delegated
> frame swap from the renderer.  These are executed in a later step, when
> the browser is composited.  Unfortunately, the browser may not be
> composited for every render frame.  This means multiple copies/readbacks
> may become enqueued, each of which is expensive, and will turn out to be
> completely redundant as the results will be identical.  This change
> detects this scenario, and de-dupes by "aborting" the older frame
> subscriber callback.
>
> BUG=464475
>
> Committed: https://crrev.com/ddee0845cc298cbba6f9d8d6ff7fb9e06073f0e8
> Cr-Commit-Position: refs/heads/master@{#319998}

TBR=danakj@chromium.org,ccameron@chromium.org,hubbe@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=464475
Committed: https://crrev.com/ca0aa371d85941c6ea66b325efa237b339e23319
Cr-Commit-Position: refs/heads/master@{#321828}

[miu, 2015-03-23 19:25:18]

Created Revert of De-dupe copy requests for tab capture in DelegatedFrameHost.

[commit-bot: I haz the power, 2015-03-23 19:26:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1010803013/1

[commit-bot: I haz the power, 2015-03-23 19:27:19]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-23 19:28:13]

Patchset 1 (id:??) landed as
https://crrev.com/ca0aa371d85941c6ea66b325efa237b339e23319
Cr-Commit-Position: refs/heads/master@{#321828}