From 248a245c95c4bd1eaaa89476c37e28c384941af9 Mon Sep 17 00:00:00 2001
From: Bobby Holley <bobbyholley@gmail.com>
Date: Thu, 10 Aug 2017 17:28:25 -0700
Subject: [PATCH] Make the parallel traversal an explicit flag instead of
 guessing from Servo.

MozReview-Commit-ID: 83DgB1sZnCb
---
 components/style/traversal_flags.rs | 5 +++++
 ports/geckolib/glue.rs              | 3 ++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/components/style/traversal_flags.rs b/components/style/traversal_flags.rs
index 7a985c3d3cf..2e3e0f4c2ad 100644
--- a/components/style/traversal_flags.rs
+++ b/components/style/traversal_flags.rs
@@ -31,6 +31,10 @@ bitflags! {
         const ClearDirtyDescendants = 1 << 5,
         /// Clears the animation-only dirty descendants bit in the subtree.
         const ClearAnimationOnlyDirtyDescendants = 1 << 6,
+        /// Allows the traversal to run in parallel if there are sufficient cores on
+        /// the machine.
+        const ParallelTraversal = 1 << 7,
+
     }
 }
 
@@ -62,6 +66,7 @@ pub fn assert_traversal_flags_match() {
         ServoTraversalFlags_ClearDirtyDescendants => ClearDirtyDescendants,
         ServoTraversalFlags_ClearAnimationOnlyDirtyDescendants =>
             ClearAnimationOnlyDirtyDescendants,
+        ServoTraversalFlags_ParallelTraversal => ParallelTraversal,
     }
 }
 
diff --git a/ports/geckolib/glue.rs b/ports/geckolib/glue.rs
index 552ee02fe61..0d0ff0db9be 100644
--- a/ports/geckolib/glue.rs
+++ b/ports/geckolib/glue.rs
@@ -229,7 +229,8 @@ fn traverse_subtree(element: GeckoElement,
     debug!("{:?}", ShowSubtreeData(element.as_node()));
 
     let style_thread_pool = &*STYLE_THREAD_POOL;
-    let traversal_driver = if style_thread_pool.style_thread_pool.is_none() || !element.is_root() {
+    let traversal_driver = if !traversal_flags.contains(traversal_flags::ParallelTraversal) ||
+                              style_thread_pool.style_thread_pool.is_none() {
         TraversalDriver::Sequential
     } else {
         TraversalDriver::Parallel