DevTools: migrate from ui-setting to settings extension point.

Source/devtools/front_end/ui/SettingsUI.js

Index: Source/devtools/front_end/ui/SettingsUI.js
diff --git a/Source/devtools/front_end/ui/SettingsUI.js b/Source/devtools/front_end/ui/SettingsUI.js
index 4892e1470b0c9660a0852f8eaf3c96e789afabc3..d723f90cbd13b2a5fb0b8c4d6f71f804fce5da08 100644
--- a/Source/devtools/front_end/ui/SettingsUI.js
+++ b/Source/devtools/front_end/ui/SettingsUI.js
@@ -273,18 +273,15 @@ WebInspector.SettingsUI.createInput = function(parentElement, id, defaultText, e
 }
 
 /**
- * @constructor
+ * @interface
  */
-WebInspector.UISettingDelegate = function()
+WebInspector.SettingUI = function()
 {
 }
 
-WebInspector.UISettingDelegate.prototype = {
+WebInspector.SettingUI.prototype = {
     /**
      * @return {?Element}
      */
-    settingElement: function()
-    {
-        return null;
-    }
+    settingElement: function() { }
 }