servo · emilio · Nov 19, 2016 · Nov 19, 2016
diff --git a/components/compositing/compositor.rs b/components/compositing/compositor.rs
@@ -1418,11 +1418,15 @@ impl<Window: WindowMethods> IOCompositor<Window> {
         };
 
         if wait_for_stable_image {
+            // If there are animations active, tick those and continue waiting
+            // for all animations to complete before bothering the
+            // constellation.
+            if self.animations_active() {
+                self.process_animations();
+                return Err(UnableToComposite::NotReadyToPaintImage(NotReadyToPaint::AnimationsActive));
+            }
             match self.is_ready_to_paint_image_output() {
                 Ok(()) => {
-                    // The current image is ready to output. However, if there are animations active,
-                    // tick those instead and continue waiting for the image output to be stable AND
-                    // all active animations to complete.
                     if self.animations_active() {
                         self.process_animations();
                         return Err(UnableToComposite::NotReadyToPaintImage(NotReadyToPaint::AnimationsActive));

diff --git a/components/constellation/constellation.rs b/components/constellation/constellation.rs
@@ -75,6 +75,7 @@ enum ReadyToSave {
     PendingFrames,
     WebFontNotLoaded,
     DocumentLoading,
+    UnknownState,
     EpochMismatch,
     PipelineUnknown,
     Ready,
@@ -2183,9 +2184,10 @@ impl<Message, LTF, STF> Constellation<Message, LTF, STF>
             // See if this pipeline has reached idle script state yet.
             match self.document_states.get(&frame.current.pipeline_id) {
                 Some(&DocumentState::Idle) => {}
-                Some(&DocumentState::Pending) | None => {
+                Some(&DocumentState::Pending) => {
                     return ReadyToSave::DocumentLoading;
                 }
+                None => return ReadyToSave::UnknownState,
             }
 
             // Check the visible rectangle for this pipeline. If the constellation has received a

diff --git a/tests/wpt/harness/wptrunner/executors/reftest-wait_servodriver.js b/tests/wpt/harness/wptrunner/executors/reftest-wait_servodriver.js
@@ -6,7 +6,8 @@
 callback = arguments[arguments.length - 1];
 
 function check_done() {
-    if (!document.body.classList.contains('reftest-wait')) {
+    if (!document.body.classList.contains('reftest-wait') &&
+        !document.documentElement.classList.contains('reftest-wait')) {
         callback();
     } else {
         setTimeout(check_done, 50);

diff --git a/tests/wpt/mozilla/tests/css/incremental_trailing_whitespace_a.html b/tests/wpt/mozilla/tests/css/incremental_trailing_whitespace_a.html
@@ -1,9 +1,10 @@
 <!doctype html>
-<html>
+<html class="reftest-wait">
   <head>
     <meta charset="utf-8">
     <title>incremental trailing whitespace test</title>
     <link rel="match" href="incremental_trailing_whitespace_ref.html">
+    <script src="/common/reftest-wait.js"></script>
     <style>
       #a {
         border: 0 solid;
@@ -20,8 +21,14 @@
     </div>
     <script>
       document.body.offsetWidth; // force layout
-      document.querySelector('#a').classList.add('go');
-      // FIXME (#10245): Wait for the "transitionend" event.
+      var div = document.getElementById('a');
+      div.addEventListener('transitionend', function() {
+        // FIXME(emilio, #13865): requestAnimationFrame shouldn't be needed.
+        requestAnimationFrame(function() {
+          document.documentElement.classList.remove('reftest-wait');
+        });
+      });
+      div.classList.add('go');
     </script>
   </body>
 </html>