Implement [Inline] interfaces

Inline interfaces just appear as a Rust type and in the TypeId hierarchy.
They are completely invisible on the JS side.

components/script/dom/webidls/GlobalScope.webidl

@@ -0,0 +1,10 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// This interface is entirely internal to Servo, and should not be accessible to
+// web pages.
+
+[Exposed=(Window,Worker),
+ Inline]
+interface GlobalScope : EventTarget {};

components/script/dom/webidls/Window.webidl

@@ -4,7 +4,7 @@
 
 // https://html.spec.whatwg.org/multipage/#window
 [PrimaryGlobal, Exposed=(Window,Worker)]
-/*sealed*/ interface Window : EventTarget {
+/*sealed*/ interface Window : GlobalScope {
   // the current browsing context
   [Unforgeable] readonly attribute WindowProxy window;
   [BinaryName="Self_", Replaceable] readonly attribute WindowProxy self;

components/script/dom/webidls/WorkerGlobalScope.webidl

@@ -4,7 +4,7 @@
 
 // https://html.spec.whatwg.org/multipage/#workerglobalscope
 [Abstract, Exposed=Worker]
-interface WorkerGlobalScope : EventTarget {
+interface WorkerGlobalScope : GlobalScope {
   [BinaryName="Self_"] readonly attribute WorkerGlobalScope self;
   readonly attribute WorkerLocation location;