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

chrome/browser/ui/webui/chrome_web_ui_controller_factory.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/ui/webui/chrome_web_ui_controller_factory.h"
 
 #include <stddef.h>
 
 #include <vector>
 
@@ skipping 392 matching lines @@
   // Otherwise, it's handled by the uber settings page.
   if (url.host() == chrome::kChromeUIExtensionsHost &&
       ::switches::MdExtensionsEnabled()) {
     return &NewWebUI<extensions::ExtensionsUI>;
   }
   // Material Design history is on its own host, rather than on an Uber page.
   if (base::FeatureList::IsEnabled(features::kMaterialDesignHistoryFeature) &&
       url.host() == chrome::kChromeUIHistoryHost) {
     return &NewWebUI<MdHistoryUI>;
   }
+  // Material Design Settings gets its own host, if enabled.
+  if (base::FeatureList::IsEnabled(features::kMaterialDesignSettingsFeature) &&
+      url.host() == chrome::kChromeUISettingsHost) {
+    return &NewWebUI<settings::MdSettingsUI>;

[Dan Beam, 2016/06/01 20:59:49]

i think it'd make sense to do one of two things here:

1) group by host
2) group by webui

i.e.

if (url is md-settings)
  return md settings

if (url is settings-frame)
  return settings

if (url is settings)
  return md if md is on, else settings

OR

if (md-settings or settings URL and md is on)
  return md

if (settings-frame or settings URL and md is off)
  return settings

[groby-ooo-7-16, 2016/06/01 23:29:35]

I'm following the established pattern - all material design switches are here :)

[Dan Beam, 2016/06/01 23:38:32]

ah, i see: UberUI creates it's own WebUIs for the subpages because it's a
special flower.  aight, this makes sense then

+  }
   if (url.host() == chrome::kChromeUIQuotaInternalsHost)
     return &NewWebUI<QuotaInternalsUI>;
   // Settings are implemented with native UI elements on Android.
   // Handle chrome://settings if settings in a window and about in settings
   // are enabled.
   if (url.host() == chrome::kChromeUISettingsFrameHost ||
       (url.host() == chrome::kChromeUISettingsHost &&
        ::switches::AboutInSettingsEnabled())) {
     return &NewWebUI<options::OptionsUI>;
   }
@@ skipping 365 matching lines @@
 #endif
 
   // Android doesn't use the plugins pages.
   if (page_url.host() == chrome::kChromeUIPluginsHost)
     return PluginsUI::GetFaviconResourceBytes(scale_factor);
 
 #endif
 
   return NULL;
 }