### Describe what you were doing when the bug occurred:
1. I did profiling on a list, that gets updated on each pagination api call.
2. Once the profiling was done, I moved around in the Profiler to view the Flamegraph
3. Moving to second capture, the Profiler crashed.


**DevTools version**: 4.6.0-6cceaeb67

```
Component stack: in ec
    in div
    in div
    in div
    in So
    in Unknown
    in n
    in Unknown
    in div
    in div
    in rl
    in Ze
    in fn
    in Ga
    in _s
```
const errorCountsMap = fiberToErrorsMap.get(fiberID);
          const warningCountsMap = fiberToWarningsMap.get(fiberID);
          if (errorCountsMap != null) {
            errorCountsMap.forEach(count => {
              errorCount += count;
            });
          }
          if (warningCountsMap != null) {
            warningCountsMap.forEach(count => {
              warningCount += count;
            });
          }
        }
        pushOperation(TREE_OPERATION_UPDATE_ERRORS_OR_WARNINGS);
        pushOperation(fiberID);
        pushOperation(errorCount);
        pushOperation(warningCount);
      }
    });
    fibersWithChangedErrorOrWarningCounts.clear();
  }
  function flushPendingEvents(root: Object): void {
     Add any pending errors and warnings to the operations array.
     We do this just before flushing, so we can ignore errors for no-longer-mounted Fibers.
    recordPendingErrorsAndWarnings();
    if (
      pendingOperations.length === 0 &&
      pendingRealUnmountedIDs.length === 0 &&
      pendingSimulatedUnmountedIDs.length === 0 &&
      pendingUnmountedRootID === null