compositor: Process animations before asking the constellation for th…

…e image.

The ready state could depend on animations being processed (as in
incremental_trailing_whitespace_a.html), and that will never happen with the
previous code.

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));

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