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

chrome/browser/browser_about_handler.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/browser_about_handler.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/single_thread_task_runner.h"
 #include "base/strings/string_util.h"
 #include "base/threading/thread_task_runner_handle.h"
 #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"
 #include "components/url_formatter/url_fixer.h"
 
 bool FixupBrowserAboutURL(GURL* url,
                           content::BrowserContext* browser_context) {
   // Ensure that any cleanup done by FixupURL happens before the rewriting
   // phase that determines the virtual URL, by including it in an initial
   // URLHandler.  This prevents minor changes from producing a virtual URL,
@@ skipping 53 matching lines @@
     } else {
 #if defined(OS_ANDROID)
       // On Android, redirect directly to chrome://history-frame since
       // uber page is unsupported.
       host = chrome::kChromeUIHistoryFrameHost;
 #else
       host = chrome::kChromeUIUberHost;
       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) {
     if (::switches::AboutInSettingsEnabled()) {
       host = chrome::kChromeUISettingsFrameHost;
       if (url->path().empty() || url->path() == "/")
         path = chrome::kChromeUIHelpHost;
     } else {
       host = chrome::kChromeUIUberHost;
       path = chrome::kChromeUIHelpHost + url->path();
@@ skipping 20 matching lines @@
         FROM_HERE, base::Bind(&chrome::AttemptRestart));
     return true;
   } else if (base::LowerCaseEqualsASCII(spec, chrome::kChromeUIQuitURL)) {
     base::ThreadTaskRunnerHandle::Get()->PostTask(
         FROM_HERE, base::Bind(&chrome::AttemptExit));
     return true;
   }
 
   return false;
 }