Bug 1419285 - Part 1. Calculate composition rect for remote XUL frame. r=masayuki

Out of process support for Web extension creates another XUL widget for it.
We should calculate correct offset for Web Extension's remote widget.

MozReview-Commit-ID: AaALzLeKLsM

--HG--
extra : rebase_source : da3562d6ec6b93b99d12b0cac4d80d8b91e286fd

dom/ipc/TabParent.cpp

@@ -2286,8 +2286,16 @@ TabParent::HandleQueryContentEvent(WidgetQueryContentEvent& aEvent)
     case eQueryTextRect:
     case eQueryCaretRect:
     case eQueryEditorRect:
+    {
+      nsCOMPtr<nsIWidget> widget = GetWidget();
+      nsCOMPtr<nsIWidget> docWidget = GetDocWidget();
+      if (widget != docWidget) {
+        aEvent.mReply.mRect +=
+          nsLayoutUtils::WidgetToWidgetOffset(widget, docWidget);
+      }
       aEvent.mReply.mRect -= GetChildProcessOffset();
       break;
+    }
     default:
       break;
   }