Cleanup and fix ResourceDispatcherHostTests.

Cleanup and fix ResourceDispatcherHostTests.

This fixes some issues introduced in 273245
(https://codereview.chromium.org/305443005)

* Forward declare test fixture before first use.  The file
  is only building because of a forward declaration in another
  file, which is going away in another CL.
* Remove unused variable.
* Add missing include.

BUG=81979
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=274616

[mmenke, 2014-06-03 16:59:11]

Could one of you two get to this pretty promptly?  It was making a CL that
modifies some net files have tryjob failures, and be nice to get this in before
anyone else runs into the issue and has to investigate.

Thanks!

[mmenke, 2014-06-03 17:32:18]

On 2014/06/03 16:59:11, mmenke wrote:
> Could one of you two get to this pretty promptly?  It was making a CL that
> modifies some net files have tryjob failures, and be nice to get this in
before
> anyone else runs into the issue and has to investigate.
> 
> Thanks!

Ahh...right...  My CL other removes the friend declaration in url_request.h, and
there's a forward declaration needed for that.  So no one else should run into
this problem.

[davidben, 2014-06-03 19:23:03]

lgtm

[mmenke, 2014-06-03 19:23:42]

On 2014/06/03 19:23:03, David Benjamin wrote:
> lgtm

Thanks!

[mmenke, 2014-06-03 19:29:14]

The CQ bit was checked by mmenke@chromium.org

[commit-bot: I haz the power, 2014-06-03 19:29:45]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/mmenke@chromium.org/310883002/1

[commit-bot: I haz the power, 2014-06-03 20:54:39]

Change committed as 274616