[MD Settings] Add feature to enable md-settings by default.

chrome/browser/browser_about_handler.cc

Index: chrome/browser/browser_about_handler.cc
diff --git a/chrome/browser/browser_about_handler.cc b/chrome/browser/browser_about_handler.cc
index 04274b19630444720285912579e02d40cfcc37a8..1ef7d85a3b6c72f1130279f9c032cf0ad07f5c84 100644
--- a/chrome/browser/browser_about_handler.cc
+++ b/chrome/browser/browser_about_handler.cc
@@ -15,6 +15,7 @@
 #include "build/build_config.h"
 #include "chrome/browser/lifetime/application_lifetime.h"
 #include "chrome/browser/ui/browser_dialogs.h"
+#include "chrome/browser/ui/chrome_pages.h"
 #include "chrome/common/chrome_features.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/url_constants.h"
@@ -88,13 +89,13 @@ bool WillHandleBrowserAboutURL(GURL* url,
       path = chrome::kChromeUIHistoryHost + url->path();
 #endif
     }
-  // Redirect chrome://settings
-  } else if (host == chrome::kChromeUISettingsHost) {
+    // Redirect legacy settings page to uber page.
+  } else if (host == chrome::GetLegacySettingsHost()) {
     if (::switches::AboutInSettingsEnabled()) {
       host = chrome::kChromeUISettingsFrameHost;
     } else {
       host = chrome::kChromeUIUberHost;
-      path = chrome::kChromeUISettingsHost + url->path();
+      path = chrome::GetLegacySettingsHost() + url->path();
     }
   // Redirect chrome://help
   } else if (host == chrome::kChromeUIHelpHost) {