Stash pendingEffectsLanes earlier

In the gap when a commit is delayed, we don't know which lanes are currently
pending. We can use the same flag as the ones we use when we're in the
middle of commit effects by setting it earlier.

This ensures that we don't write an "Animating" track during this period
since it'll get some other suspended/delay track logged (for example
"waiting on previous animation".

Author: sebmarkbage

packages/react-reconciler/src/ReactFiberWorkLoop.js

@@ -1438,6 +1438,7 @@ function finishConcurrentRender(
         // immediately, wait for more data to arrive.
         // TODO: Combine retry throttling with Suspensey commits. Right now they
         // run one after the other.
+        pendingEffectsLanes = lanes;
         root.timeoutHandle = scheduleTimeout(
           commitRootWhenReady.bind(
             null,
@@ -1551,6 +1552,7 @@ function commitRootWhenReady(
       // Not yet ready to commit. Delay the commit until the renderer notifies
       // us that it's ready. This will be canceled if we start work on the
       // root again.
+      pendingEffectsLanes = lanes;
       root.cancelPendingCommit = schedulePendingCommit(
         commitRoot.bind(
           null,
@@ -2093,6 +2095,8 @@ function prepareFreshStack(root: FiberRoot, lanes: Lanes): Fiber {
     cancelPendingCommit();
   }
 
+  pendingEffectsLanes = NoLanes;
+
   resetWorkInProgressStack();
   workInProgressRoot = root;
   const rootWorkInProgress = createWorkInProgress(root.current, null);