Reland of Fall back to default media device from preferences if no default is supplied from the c...

chrome/browser/media/webrtc/webrtc_apprtc_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 "base/command_line.h"
 #include "base/files/file_enumerator.h"
 #include "base/path_service.h"
 #include "base/process/launch.h"
 #include "base/rand_util.h"
 #include "build/build_config.h"
@@ skipping 34 matching lines @@
 // call gets up when connecting to the same room from two tabs in a browser.
 class WebRtcApprtcBrowserTest : public WebRtcTestBase {
  public:
   WebRtcApprtcBrowserTest() {}
 
   void SetUpCommandLine(base::CommandLine* command_line) override {
     EXPECT_FALSE(command_line->HasSwitch(switches::kUseFakeUIForMediaStream));
 
     // The video playback will not work without a GPU, so force its use here.
     command_line->AppendSwitch(switches::kUseGpuInTests);
-    base::CommandLine::ForCurrentProcess()->AppendSwitch(
-        switches::kUseFakeDeviceForMediaStream);
+    // This test fails on some Mac bots if no default devices are specified on
+    // the command line.
+    base::CommandLine::ForCurrentProcess()->AppendSwitchASCII(
+        switches::kUseFakeDeviceForMediaStream,
+        "audio-input-default-id=default,video-input-default-id=default");
   }
 
   void TearDown() override {
     // Kill any processes we may have brought up. Note: this isn't perfect,
     // especially if the test hangs or if we're on Windows.
     LOG(INFO) << "Entering TearDown";
     if (dev_appserver_.IsValid())
       dev_appserver_.Terminate(0, false);
     if (collider_server_.IsValid())
       collider_server_.Terminate(0, false);
@@ skipping 229 matching lines @@
       InfoBarService::FromWebContents(chrome_tab), InfoBarResponder::ACCEPT);
   ui_test_utils::NavigateToURL(browser(), room_url);
 
   ASSERT_TRUE(LaunchFirefoxWithUrl(room_url));
 
   ASSERT_TRUE(WaitForCallToComeUp(chrome_tab));
 
   // Ensure Firefox manages to send video our way.
   ASSERT_TRUE(DetectRemoteVideoPlaying(chrome_tab));
 }