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..4a4daa1566c91c6129381781f9c4f4c7c1e1611e 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"
@@ -69,7 +70,13 @@ namespace extensions {
 
 class WebViewMediaAccessAPITest : public WebViewAPITest {
  protected:
-  WebViewMediaAccessAPITest() {}
+  WebViewMediaAccessAPITest() {
+    // This switch ensures that there will always be at least one media device,
+    // even on machines without physical devices. This is required for tests
+    // that request permission to use media devices.
+    base::CommandLine::ForCurrentProcess()->AppendSwitch(

[Marijn Kruisselbrink, 2017/04/11 18:02:17]

nit: To add command line flags you should probably override SetUpCommandLine
(make sure you still call WebViewAPITest::SetUpCommandLine as well of course),
rather than doing this in the constructor.

+        "use-fake-device-for-media-stream");
+  }
 
   // Runs media_access tests.
   void RunTest(const std::string& test_name) {