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..484e0e847a9da1f8a344a40a3aa6770ff1caa44b 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) {
+  std::string default_audio_capture_1("test_default_audio_capture");

[Peter Kasting, 2017/01/24 00:39:17]

Nit: Prefer = to () for initializing strings; see
https://www.chromium.org/developers/coding-style/cpp-dos-and-donts#TOC-Variab...
(several places)

Consider using const and naming these kConstantStyle, since these are
compile-time constants.  (Can't use constexpr with std::string.)

[Guido Urdaneta, 2017/01/24 09:31:35]

Done.

+  std::string default_video_capture_1("test_default_video_capture");
+  browser()->profile()->GetPrefs()->SetString(prefs::kDefaultAudioCaptureDevice,
+                                              default_audio_capture_1);
+  browser()->profile()->GetPrefs()->SetString(prefs::kDefaultVideoCaptureDevice,
+                                              default_video_capture_1);

[Peter Kasting, 2017/01/24 00:39:17]

Nit: Optional, but if you use a lambda here, you can reduce the boilerplate in
these SetString() calls:

  auto SetString = [this](const std::string& path, const std::string& value) {
    browser()->profile()->GetPrefs()->SetString(path, value);
  }
  SetString(prefs::kDefaultAudioCaptureDevice, default_audio_capture_1);
  ...

(overall this is one line shorter)

[Guido Urdaneta, 2017/01/24 09:31:35]

Done.

+  ui_test_utils::NavigateToURL(browser(), GURL("chrome://newtab"));
+  WebContents* web_contents =
+      browser()->tab_strip_model()->GetActiveWebContents();
+  EXPECT_EQ(default_audio_capture_1,
+            web_contents->GetDelegate()->GetDefaultMediaDeviceID(
+                web_contents, content::MEDIA_DEVICE_AUDIO_CAPTURE));

[Peter Kasting, 2017/01/24 00:39:17]

Nit: Optional, but if you use a lambda here, you can reduce the boilerplate in
these EXPECTs:

  auto GetDeviceID = [web_contents](content::MediaStreamType type) {
    return web_contents->GetDelegate()->GetDefaultMediaDeviceID(web_contents,
                                                                type);
  }
  EXPECT_EQ(default_audio_capture_1,
            GetDeviceID(content::MEDIA_DEVICE_AUDIO_CAPTURE));
  ...

(overall this is the same number of lines)

[Guido Urdaneta, 2017/01/24 09:31:35]

Done.

+  EXPECT_EQ(default_video_capture_1,
+            web_contents->GetDelegate()->GetDefaultMediaDeviceID(
+                web_contents, content::MEDIA_DEVICE_VIDEO_CAPTURE));
+
+  std::string default_audio_capture_2("test_default_audio_capture_2");
+  std::string default_video_capture_2("test_default_video_capture_2");
+  browser()->profile()->GetPrefs()->SetString(prefs::kDefaultAudioCaptureDevice,
+                                              default_audio_capture_2);
+  browser()->profile()->GetPrefs()->SetString(prefs::kDefaultVideoCaptureDevice,
+                                              default_video_capture_2);
+  EXPECT_EQ(default_audio_capture_2,
+            web_contents->GetDelegate()->GetDefaultMediaDeviceID(
+                web_contents, content::MEDIA_DEVICE_AUDIO_CAPTURE));
+  EXPECT_EQ(default_video_capture_2,
+            web_contents->GetDelegate()->GetDefaultMediaDeviceID(
+                web_contents, content::MEDIA_DEVICE_VIDEO_CAPTURE));
+}
+
 namespace {
 class JSBooleanResultGetter {
  public: