Correcting recording time in WebRTC AQ test.

I forgot the WebAudio case when I increased the silence lead-in;
increase that time by five seconds also.

BUG=480798,477653

Review URL: https://codereview.chromium.org/1105853002

Cr-Commit-Position: refs/heads/master@{#326779}

chrome/browser/media/chrome_webrtc_audio_quality_browsertest.cc

@@ -687,10 +687,10 @@ IN_PROC_BROWSER_TEST_F(MAYBE_WebRtcAudioQualityBrowserTest,
 
   base::FilePath recording = CreateTemporaryWaveFile();
 
-  // Note: the sound clip is about 13 seconds: record for 20 seconds to get some
+  // Note: the sound clip is 21.6 seconds: record for 25 seconds to get some
   // safety margins on each side.
   AudioRecorder recorder;
-  ASSERT_TRUE(recorder.StartRecording(base::TimeDelta::FromSeconds(20),
+  ASSERT_TRUE(recorder.StartRecording(base::TimeDelta::FromSeconds(25),
                                       recording));
 
   PlayAudioFileThroughWebAudio(left_tab);