Issue #1118 - Part 5: Change the way document.open() works

This changes the work we do for document.open() in the following ways:
- We no longer create a new Window when doing document.open().
  We use the same Window but remove all the event listeners on the
  existing DOM tree and Window before removing the document's existing
  children to provide a clean slate document to use for .write().
- We no longer create a session history entry (previously would be a
  wyciwyg URI). We now replace the current one, effectively losing the
  entry for the original document.
- We now support document.open() on windowless documents.

dom/base/nsIDocument.h

@@ -1448,7 +1448,7 @@ public:
   virtual void EndLoad() = 0;
 
   enum ReadyState { READYSTATE_UNINITIALIZED = 0, READYSTATE_LOADING = 1, READYSTATE_INTERACTIVE = 3, READYSTATE_COMPLETE = 4};
-  virtual void SetReadyStateInternal(ReadyState rs) = 0;
+  virtual void SetReadyStateInternal(ReadyState rs, bool updateTimingInformation = true) = 0;
   ReadyState GetReadyStateEnum()
   {
     return mReadyState;
@@ -2186,6 +2186,19 @@ public:
     mAllowXULXBL = eTriTrue;
   }
 
+  /**
+   * Flag whether we're about to fire the window's load event for this document.
+   */
+  virtual void SetLoadEventFiring(bool aFiring) = 0;
+
+  /**
+   * Test whether we should be firing a load event for this document after a
+   * document.close().
+   * This method should only be called at the point when the load event is about
+   * to be fired, since it resets `skip`.
+   */
+  virtual bool SkipLoadEventAfterClose() = 0;
+
   /**
    * Returns the template content owner document that owns the content of
    * HTMLTemplateElement.