From 99bece105f07fd2a72194c20b9e0d6f9fd38ed23 Mon Sep 17 00:00:00 2001
From: Cameron Kaiser <classilla@floodgap.com>
Date: Mon, 7 Jan 2019 20:06:28 -0800
Subject: [PATCH] M1338678

---
 layout/base/nsCSSFrameConstructor.cpp | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/layout/base/nsCSSFrameConstructor.cpp b/layout/base/nsCSSFrameConstructor.cpp
index c33dab312..67909380e 100644
--- a/layout/base/nsCSSFrameConstructor.cpp
+++ b/layout/base/nsCSSFrameConstructor.cpp
@@ -6727,8 +6727,11 @@ nsCSSFrameConstructor::MaybeConstructLazily(Operation aOperation,
                                             nsIContent* aContainer,
                                             nsIContent* aChild)
 {
+  // XXXmats no lazy frames for display:contents direct descendants yet
+  // (bug 979782).
   if (mPresShell->GetPresContext()->IsChrome() || !aContainer ||
-      aContainer->IsInNativeAnonymousSubtree() || aContainer->IsXULElement()) {
+      aContainer->IsInNativeAnonymousSubtree() || aContainer->IsXULElement() ||
+      GetDisplayContentsStyleFor(aContainer)) {
     return false;
   }
 
@@ -6756,12 +6759,17 @@ nsCSSFrameConstructor::MaybeConstructLazily(Operation aOperation,
 
   // Walk up the tree setting the NODE_DESCENDANTS_NEED_FRAMES bit as we go.
   nsIContent* content = aContainer;
+
 #ifdef DEBUG
   // If we hit a node with no primary frame, or the NODE_NEEDS_FRAME bit set
   // we want to assert, but leaf frames that process their own children and may
   // ignore anonymous children (eg framesets) make this complicated. So we set
   // these two booleans if we encounter these situations and unset them if we
   // hit a node with a leaf frame.
+  //
+  // Also, it's fine if one of the nodes without primary frame is a display:
+  // contents node except if it's the direct ancestor of the children we're
+  // recreating frames for.
   bool noPrimaryFrame = false;
   bool needsFrameBitSet = false;
 #endif
@@ -6771,17 +6779,14 @@ nsCSSFrameConstructor::MaybeConstructLazily(Operation aOperation,
     if (content->GetPrimaryFrame() && content->GetPrimaryFrame()->IsLeaf()) {
       noPrimaryFrame = needsFrameBitSet = false;
     }
-    if (!noPrimaryFrame && !content->GetPrimaryFrame()) {
+    if (!noPrimaryFrame && !content->GetPrimaryFrame() &&
+        !GetDisplayContentsStyleFor(content)) {
       noPrimaryFrame = true;
     }
     if (!needsFrameBitSet && content->HasFlag(NODE_NEEDS_FRAME)) {
       needsFrameBitSet = true;
     }
 #endif
-    // XXXmats no lazy frames for display:contents descendants yet (bug 979782).
-    if (GetDisplayContentsStyleFor(content)) {
-      return false;
-    }
     content->SetFlags(NODE_DESCENDANTS_NEED_FRAMES);
     content = content->GetFlattenedTreeParent();
   }