Bug 1761938 - Part 4: Give module loaders a global object field r=smaug,yulia

This gives the module loader a field for the current global, since a module map
is only associated with a single global.

This adds a method to Document to tell the script loader when its global
changes. I'm not sure of when we do this exactly.

Differential Revision: https://phabricator.services.mozilla.com/D142831

dom/script/ScriptLoader.h

@@ -132,6 +132,12 @@ class ScriptLoader final : public JS::loader::ScriptLoaderInterface {
   NS_DECL_CYCLE_COLLECTING_ISUPPORTS
   NS_DECL_CYCLE_COLLECTION_CLASS(ScriptLoader)
 
+  /**
+   * Called when the document that owns this script loader changes global. The
+   * argument is null when the document is detached from a window.
+   */
+  void SetGlobalObject(nsIGlobalObject* aGlobalObject);
+
   /**
    * The loader maintains a weak reference to the document with
    * which it is initialized. This call forces the reference to
@@ -322,7 +328,7 @@ class ScriptLoader final : public JS::loader::ScriptLoaderInterface {
   /**
    * Returns wether any request is queued, and not executed yet.
    */
-  bool HasPendingRequests();
+  bool HasPendingRequests() const;
 
   /**
    * Returns wether there are any dynamic module import requests pending.