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

Review URL: https://codereview.chromium.org/310883002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@274616 0039d316-1c4b-4281-b951-d872f2087c98

content/browser/loader/resource_dispatcher_host_unittest.cc

@@ -45,6 +45,7 @@
 #include "net/url_request/url_request.h"
 #include "net/url_request/url_request_context.h"
 #include "net/url_request/url_request_job.h"
+#include "net/url_request/url_request_job_factory.h"
 #include "net/url_request/url_request_simple_job.h"
 #include "net/url_request/url_request_test_job.h"
 #include "net/url_request/url_request_test_util.h"
@@ -460,10 +461,12 @@ class URLRequestBigJob : public net::URLRequestSimpleJob {
   }
 };
 
+class ResourceDispatcherHostTest;
+
 class TestURLRequestJobFactory : public net::URLRequestJobFactory {
  public:
-  explicit TestURLRequestJobFactory(ResourceDispatcherHostTest* test_fixture) :
-      test_fixture_(test_fixture),
+  explicit TestURLRequestJobFactory(ResourceDispatcherHostTest* test_fixture)
+      : test_fixture_(test_fixture),
         delay_start_(false),
         delay_complete_(false),
         network_start_notification_(false),