Auto merge of #15160 - emilio:expose-traversal-kind, r=bholley

style: Expose the traversal kind to the style system.

This way we'll be able to take different paths for the sequential and parallel
traversals in some concrete cases.

This is a preliminar patch to fix bug 1332525.

r? @bholley

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1 files changed, 10 insertions, 3 deletions

diff --git a/components/layout_thread/lib.rs b/components/layout_thread/lib.rs
index 19c86f64fff..caabb158f5d 100644
--- a/components/layout_thread/lib.rs
+++ b/components/layout_thread/lib.rs
@@ -121,7 +121,7 @@ use style::stylesheets::{Origin, Stylesheet, UserAgentStylesheets};
 use style::stylist::Stylist;
 use style::thread_state;
 use style::timer::Timer;
-use style::traversal::DomTraversal;
+use style::traversal::{DomTraversal, TraversalDriver};
 
 /// Information needed by the layout thread.
 pub struct LayoutThread {
@@ -1159,7 +1159,13 @@ impl LayoutThread {
                                                                          data.reflow_info.goal);
 
         // NB: Type inference falls apart here for some reason, so we need to be very verbose. :-(
-        let traversal = RecalcStyleAndConstructFlows::new(shared_layout_context);
+        let traversal_driver = if self.parallel_flag && self.parallel_traversal.is_some() {
+            TraversalDriver::Parallel
+        } else {
+            TraversalDriver::Sequential
+        };
+
+        let traversal = RecalcStyleAndConstructFlows::new(shared_layout_context, traversal_driver);
         let dom_depth = Some(0); // This is always the root node.
         let token = {
             let stylist = &<RecalcStyleAndConstructFlows as
@@ -1175,7 +1181,8 @@ impl LayoutThread {
                     self.time_profiler_chan.clone(),
                     || {
                 // Perform CSS selector matching and flow construction.
-                if let (true, Some(pool)) = (self.parallel_flag, self.parallel_traversal.as_mut()) {
+                if traversal_driver.is_parallel() {
+                    let pool = self.parallel_traversal.as_mut().unwrap();
                     // Parallel mode
                     parallel::traverse_dom::<ServoLayoutElement, RecalcStyleAndConstructFlows>(
                         &traversal, element, dom_depth, token, pool);