From 5358043005598da7251ff673493de0017dce2544 Mon Sep 17 00:00:00 2001
From: sotaro <sotaro.ikeda.g@gmail.com>
Date: Tue, 9 Nov 2021 22:58:10 +0000
Subject: [PATCH] Bug 1739930 - Disable CompositorSession in popup parent
 widget r=gfx-reviewers,bradwerth

From nsDocumentViewer::ShouldAttachToTopLevel(), content rendering of popup is always done by child widget.

Differential Revision: https://phabricator.services.mozilla.com/D130714
---
 widget/windows/nsWindow.cpp | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/widget/windows/nsWindow.cpp b/widget/windows/nsWindow.cpp
index 201f519673a1..43221a55dd39 100644
--- a/widget/windows/nsWindow.cpp
+++ b/widget/windows/nsWindow.cpp
@@ -7361,6 +7361,13 @@ bool nsWindow::ShouldUseOffMainThreadCompositing() {
     return false;
   }
 
+  // Content rendering of popup is always done by child window.
+  // See nsDocumentViewer::ShouldAttachToTopLevel().
+  if (mWindowType == eWindowType_popup && !mIsChildWindow) {
+    MOZ_ASSERT(!mParent);
+    return false;
+  }
+
   return nsBaseWidget::ShouldUseOffMainThreadCompositing();
 }