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

chrome/browser/ui/webui/chrome_web_ui_controller_factory.cc

Index: chrome/browser/ui/webui/chrome_web_ui_controller_factory.cc
diff --git a/chrome/browser/ui/webui/chrome_web_ui_controller_factory.cc b/chrome/browser/ui/webui/chrome_web_ui_controller_factory.cc
index 1085b740a2247975eb87dfb9890a99279c1b5000..6f2d5c3422bf2a1df556be8554826ca9b2abf8e2 100644
--- a/chrome/browser/ui/webui/chrome_web_ui_controller_factory.cc
+++ b/chrome/browser/ui/webui/chrome_web_ui_controller_factory.cc
@@ -410,6 +410,11 @@ WebUIFactoryFunction GetWebUIFactoryFunction(WebUI* web_ui,
       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.