Bug 1363864 - Add MozBeforeInitialXULLayout event. r=smaug

MozReview-Commit-ID: FPWIyAR1ocq

--HG--
extra : rebase_source : 37199ee376e7b7db8984455d965fc78996cc0f3f

dom/xul/XULDocument.cpp

@@ -3025,6 +3025,12 @@ XULDocument::DoneWalking()
             }
         }
 
+        nsContentUtils::DispatchTrustedEvent(this,
+                static_cast<nsIDocument*>(this),
+                NS_LITERAL_STRING("MozBeforeInitialXULLayout"),
+                true,
+                false);
+
         StartLayout();
 
         if (mIsWritingFastLoad && IsChromeURI(mDocumentURI))