APM in Audio Service: Fix render delay calculation

The render delay is calculated backwards, making it negative. The
time we're comparing with is in the future, not the past.

Bug: 889494
Change-Id: I3aa8b64096caa9ad5feadcafc1df5bca8e035750
Reviewed-on: https://chromium-review.googlesource.com/1246163Reviewed-by: Max Morin <maxmorin@chromium.org>
Commit-Queue: Oskar Sundbom <ossu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594648}

media/webrtc/audio_processor.cc

@@ -106,7 +106,7 @@ void AudioProcessor::AnalyzePlayout(const AudioBus& audio,
   if (!audio_processing_)
     return;
 
-  render_delay_ = base::TimeTicks::Now() - playout_time;
+  render_delay_ = playout_time - base::TimeTicks::Now();
 
   constexpr int kMaxChannels = 2;
   DCHECK_GE(parameters.channels(), 1);