Fixes in response to code review

Author: flarnie

packages/react-reconciler/src/ReactDebugFiberPerf.js

@@ -387,7 +387,7 @@ export function stopWorkLoopTimer(
     commitCountInCurrentWorkLoop = 0;
     let label = didCompleteRoot
       ? '(React Tree Reconciliation: Completed Root)'
-      : '(React Tree Reconciliation)';
+      : '(React Tree Reconciliation: Yielded)';
     // Pause any measurements until the next loop.
     pauseTimers();
     endMark(label, '(React Tree Reconciliation)', warning);

packages/react-reconciler/src/ReactFiberScheduler.js

@@ -876,31 +876,41 @@ export default function<T, P, I, TI, HI, PI, C, CC, CX, PL>(
     } while (true);
 
     // We're done performing work. Time to clean up.
-    const didCompleteRoot = nextUnitOfWork === null && isRootReadyForCommit;
-    stopWorkLoopTimer(interruptedBy, didCompleteRoot);
-    interruptedBy = null;
-    isWorking = false;
+    let didCompleteRoot = null;
 
     // Yield back to main thread.
     if (didFatal) {
+      stopWorkLoopTimer(interruptedBy, didCompleteRoot);
+      interruptedBy = null;
+      isWorking = false;
       // There was a fatal error.
       return null;
     } else if (nextUnitOfWork === null) {
       // We reached the root.
       if (isRootReadyForCommit) {
+        didCompleteRoot = true;
+        stopWorkLoopTimer(interruptedBy, didCompleteRoot);
+        interruptedBy = null;
+        isWorking = false;
         // The root successfully completed. It's ready for commit.
         root.pendingCommitExpirationTime = expirationTime;
         const finishedWork = root.current.alternate;
         return finishedWork;
       } else {
         // The root did not complete.
+        stopWorkLoopTimer(interruptedBy, didCompleteRoot);
+        interruptedBy = null;
+        isWorking = false;
         invariant(
           false,
           'Expired work should have completed. This error is likely caused ' +
             'by a bug in React. Please file an issue.',
         );
       }
     } else {
+      stopWorkLoopTimer(interruptedBy, didCompleteRoot);
+      interruptedBy = null;
+      isWorking = false;
       // There's more work to do, but we ran out of time. Yield back to
       // the renderer.
       return null;