Add functionality to get default media device IDs from user preferences.

chrome/browser/ui/browser_browsertest.cc

Index: chrome/browser/ui/browser_browsertest.cc
diff --git a/chrome/browser/ui/browser_browsertest.cc b/chrome/browser/ui/browser_browsertest.cc
index cbe4be59970a3b4bb78d4626c68cacf7415ebb77..706b88bf61bbcb68a08b91b5b4e37ef225a6c223 100644
--- a/chrome/browser/ui/browser_browsertest.cc
+++ b/chrome/browser/ui/browser_browsertest.cc
@@ -2755,6 +2755,37 @@ IN_PROC_BROWSER_TEST_F(BrowserTest, CanDuplicateTab) {
   EXPECT_TRUE(chrome::CanDuplicateTabAt(browser(), 1));
 }
 
+IN_PROC_BROWSER_TEST_F(BrowserTest, DefaultMediaDevices) {
+  const std::string kDefaultAudioCapture1 = "test_default_audio_capture";
+  const std::string kDefaultVideoCapture1 = "test_default_video_capture";
+  auto SetString = [this](const std::string& path, const std::string& value) {
+    browser()->profile()->GetPrefs()->SetString(path, value);
+  };
+  SetString(prefs::kDefaultAudioCaptureDevice, kDefaultAudioCapture1);
+  SetString(prefs::kDefaultVideoCaptureDevice, kDefaultVideoCapture1);
+
+  ui_test_utils::NavigateToURL(browser(), GURL("chrome://newtab"));
+  WebContents* web_contents =
+      browser()->tab_strip_model()->GetActiveWebContents();
+  auto GetDeviceID = [web_contents](content::MediaStreamType type) {
+    return web_contents->GetDelegate()->GetDefaultMediaDeviceID(web_contents,
+                                                                type);
+  };
+  EXPECT_EQ(kDefaultAudioCapture1,
+            GetDeviceID(content::MEDIA_DEVICE_AUDIO_CAPTURE));
+  EXPECT_EQ(kDefaultVideoCapture1,
+            GetDeviceID(content::MEDIA_DEVICE_VIDEO_CAPTURE));
+
+  const std::string kDefaultAudioCapture2 = "test_default_audio_capture_2";
+  const std::string kDefaultVideoCapture2 = "test_default_video_capture_2";
+  SetString(prefs::kDefaultAudioCaptureDevice, kDefaultAudioCapture2);
+  SetString(prefs::kDefaultVideoCaptureDevice, kDefaultVideoCapture2);
+  EXPECT_EQ(kDefaultAudioCapture2,
+            GetDeviceID(content::MEDIA_DEVICE_AUDIO_CAPTURE));
+  EXPECT_EQ(kDefaultVideoCapture2,
+            GetDeviceID(content::MEDIA_DEVICE_VIDEO_CAPTURE));
+}
+
 namespace {
 class JSBooleanResultGetter {
  public: