Reland of Use spec-compliant algorithm to select video devices in getUserMedia.

extensions/browser/guest_view/app_view/app_view_apitest.cc

Index: extensions/browser/guest_view/app_view/app_view_apitest.cc
diff --git a/extensions/browser/guest_view/app_view/app_view_apitest.cc b/extensions/browser/guest_view/app_view/app_view_apitest.cc
index 43f997e6f924d01b7451d6103532a2ae0d1305d1..ffa70202ff4f8f9b993d68f19eae00b6a7667b42 100644
--- a/extensions/browser/guest_view/app_view/app_view_apitest.cc
+++ b/extensions/browser/guest_view/app_view/app_view_apitest.cc
@@ -146,6 +146,10 @@ class AppViewTest : public AppShellTest,
 
   void SetUpCommandLine(base::CommandLine* command_line) override {
     AppShellTest::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");
 
     bool use_cross_process_frames_for_guests = GetParam();
     if (use_cross_process_frames_for_guests) {