Backed out changeset dc6dc0fd83e9 (bug 1427635) for causing geckoview-junit failures. CLOSED TREE

layout/base/nsLayoutUtils.cpp

@@ -1291,11 +1291,8 @@ int32_t nsLayoutUtils::DoCompareTreePosition(
   }
 
   AutoTArray<nsIFrame*, 20> frame1Ancestors;
-  // Note that the order of the condition is important. We need to fill the
-  // ancestors even if aCommonAncestor is null, otherwise the code below makes
-  // no sense.
-  if (!FillAncestors(aFrame1, aCommonAncestor, &frame1Ancestors) &&
-      aCommonAncestor) {
+  if (aCommonAncestor &&
+      !FillAncestors(aFrame1, aCommonAncestor, &frame1Ancestors)) {
     // We reached the root of the frame tree ... if aCommonAncestor was set,
     // it is wrong
     return DoCompareTreePosition(aFrame1, aFrame2, aIf1Ancestor, aIf2Ancestor,