Bug 1533782. Make nsISelectionController [builtinclass]. r=masayuki

Differential Revision: https://phabricator.services.mozilla.com/D22840

--HG--
extra : moz-landing-system : lando

dom/base/nsISelectionController.idl

@@ -21,7 +21,7 @@ interface nsISelectionDisplay;
 webidl Node;
 webidl Selection;
 
-[scriptable, uuid(3801c9d4-8e69-4bfc-9edb-b58278621f8f)]
+[builtinclass, scriptable, uuid(3801c9d4-8e69-4bfc-9edb-b58278621f8f)]
 interface nsISelectionController : nsISelectionDisplay
 {
    // RawSelectionType values: