Reland "Re-enable webrtc audio quality browsertests on windows."

This is a reland of a3ec8289

Original change's description:
> Re-enable webrtc audio quality browsertests on windows.
> 
> Tests were previously disabled when they started failing (more context in linked bug). Re-enabling because tests pass locally on win7 machine.
> 
> Bug: 850936
> Change-Id: Ie1ab4e82daf2c0265e932237d3edf6b3399ee803
> Reviewed-on: https://chromium-review.googlesource.com/1139066
> Reviewed-by: Henrik Boström <hbos@chromium.org>
> Commit-Queue: Marina Ciocea <marinaciocea@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#575638}

Bug: 850936
Change-Id: I44be2227ffed90d25549669de4dd3f354a98d92a
Reviewed-on: https://chromium-review.googlesource.com/1156224Reviewed-by: Henrik Boström <hbos@chromium.org>
Commit-Queue: Marina Ciocea <marinaciocea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579344}

chrome/browser/media/webrtc/webrtc_audio_quality_browsertest.cc

@@ -66,8 +66,7 @@ const int kMaxAgcSegmentDiffMs =
   200;
 #endif
 
-// Temporarily disabled on Win (https://crbug.com/850936).
-#if defined(OS_LINUX) || defined(OS_MACOSX)
+#if defined(OS_LINUX) || defined(OS_WIN) || defined(OS_MACOSX)
 #define MAYBE_WebRtcAudioQualityBrowserTest WebRtcAudioQualityBrowserTest
 #else
 // Not implemented on Android, ChromeOS etc.