Fixing perf regression caused by refactoring full stack tests

Calling CreateCapturer after CreateStreams. The wrong order of calling those methods seems to have caused perf regressions.

Testing has been done here: https://codereview.webrtc.org/1371113004/

BUG=chromium:534220

Review URL: https://codereview.webrtc.org/1394463002

Cr-Commit-Position: refs/heads/master@{#10212}
diff --git a/webrtc/video/video_quality_test.cc b/webrtc/video/video_quality_test.cc
index c0f5754..1513b81 100644
--- a/webrtc/video/video_quality_test.cc
+++ b/webrtc/video/video_quality_test.cc
@@ -783,12 +783,12 @@
   if (params.screenshare.enabled)
     SetupScreenshare(params);
 
-  CreateCapturer(params, &analyzer);
-
   CreateStreams();
   analyzer.input_ = send_stream_->Input();
   analyzer.send_stream_ = send_stream_;
 
+  CreateCapturer(params, &analyzer);
+
   send_stream_->Start();
   for (size_t i = 0; i < receive_streams_.size(); ++i)
     receive_streams_[i]->Start();
@@ -842,10 +842,9 @@
     SetupScreenshare(params);
 
   send_stream_ = call->CreateVideoSendStream(send_config_, encoder_config_);
-  CreateCapturer(params, send_stream_->Input());
-
   VideoReceiveStream* receive_stream =
       call->CreateVideoReceiveStream(receive_configs_[0]);
+  CreateCapturer(params, send_stream_->Input());
 
   receive_stream->Start();
   send_stream_->Start();