Reland of Initialize default audio device ID with explicit device ID.

extensions/browser/guest_view/web_view/web_view_media_access_apitest.cc

Index: extensions/browser/guest_view/web_view/web_view_media_access_apitest.cc
diff --git a/extensions/browser/guest_view/web_view/web_view_media_access_apitest.cc b/extensions/browser/guest_view/web_view/web_view_media_access_apitest.cc
index c013665c062d2e4c75d6d37fa6eb353ef9142c9f..2ee74f7d4f63ce4bc08d4bc299de4c48091aa542 100644
--- a/extensions/browser/guest_view/web_view/web_view_media_access_apitest.cc
+++ b/extensions/browser/guest_view/web_view/web_view_media_access_apitest.cc
@@ -2,6 +2,7 @@
 // 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/macros.h"
 #include "base/strings/stringprintf.h"
 #include "content/public/browser/web_contents_delegate.h"
@@ -80,6 +81,14 @@ class WebViewMediaAccessAPITest : public WebViewAPITest {
         base::StringPrintf("runTest('%s');", test_name.c_str())));
     ASSERT_TRUE(test_run_listener.WaitUntilSatisfied());
   }
+
+  void SetUpCommandLine(base::CommandLine* command_line) override {
+    WebViewAPITest::SetUpCommandLine(command_line);
+    // This switch ensures that there will always be at least one media device,
+    // even on machines without physical devices. This is required by tests that
+    // request permission to use media devices.
+    command_line->AppendSwitch("use-fake-device-for-media-stream");
+  }
 };
 
 IN_PROC_BROWSER_TEST_F(WebViewMediaAccessAPITest, TestAllow) {