Fix a test failure when IP Permission check is turned on

chrome/browser/media/chrome_webrtc_audio_quality_browsertest.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <ctime>
 
 #include "base/command_line.h"
 #include "base/files/file_enumerator.h"
 #include "base/files/file_util.h"
 #include "base/files/scoped_temp_dir.h"
@@ skipping 119 matching lines @@
   }
 
   void SetUpCommandLine(base::CommandLine* command_line) override {
     EXPECT_FALSE(command_line->HasSwitch(
         switches::kUseFakeUIForMediaStream));
 
     // The WebAudio-based tests don't care what devices are available to
     // getUserMedia, and the getUserMedia-based tests will play back a file
     // through the fake device using using --use-file-for-fake-audio-capture.
     command_line->AppendSwitch(switches::kUseFakeDeviceForMediaStream);
+
+    // Add loopback interface such that there is always connectivity.
+    command_line->AppendSwitch(switches::kAllowLoopbackInPeerConnection);
   }
 
   void ConfigureFakeDeviceToPlayFile(const base::FilePath& wav_file_path) {
     base::CommandLine::ForCurrentProcess()->AppendSwitchPath(
         switches::kUseFileForFakeAudioCapture, wav_file_path);
   }
 
   void AddAudioFileToWebAudio(const std::string& input_file_relative_url,
                               content::WebContents* tab_contents) {
     // This calls into webaudio.js.
@@ skipping 645 matching lines @@
 }
 
 // Since the AGC is off here there should be no gain at all.
 IN_PROC_BROWSER_TEST_F(MAYBE_WebRtcAudioQualityBrowserTest,
                        MANUAL_TestAutoGainIsOffWithAudioProcessingOff) {
   const char* kAudioCallWithoutAudioProcessing =
       "{audio: { mandatory: { echoCancellation: false } } }";
   ASSERT_NO_FATAL_FAILURE(TestAutoGainControl(
       kReferenceFile, kAudioCallWithoutAudioProcessing, "_no_agc"));
 }