[Extensions Page MD] Stub out a materialized extensions page

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 cb00c1c82b5157b79e1a017d5741bb88cbcbbb94..f1092afface7e2d9d9a8a9b21de00e5866a086dd 100644
--- a/chrome/browser/ui/webui/chrome_web_ui_controller_factory.cc
+++ b/chrome/browser/ui/webui/chrome_web_ui_controller_factory.cc
@@ -398,6 +398,12 @@ WebUIFactoryFunction GetWebUIFactoryFunction(WebUI* web_ui,
       ::switches::MdSettingsEnabled()) {
     return &NewWebUI<settings::MdSettingsUI>;
   }
+  // If the material design extensions page is enabled, it gets its own host.
+  // Otherwise, it's handled by the uber settings page.
+  if (url.host() == chrome::kChromeUIExtensionsHost &&
+      ::switches::MdExtensionsEnabled()) {
+    return &NewWebUI<extensions::ExtensionsUI>;
+  }
   if (url.host() == chrome::kChromeUIQuotaInternalsHost)
     return &NewWebUI<QuotaInternalsUI>;
   // Settings are implemented with native UI elements on Android.