Hi, long time user, first time issuer.

I think I found a bug with the Profiler component. When I click on the `Save profile...` button at the top nothing happens and there appears to be no new files in my Downloads folder. I think it might be silently failing and that's why I am not getting any response.  Has anyone else ran into this issue?

Another thing I would like to mention is that I haven't looked through all of the documentation material about the new Profiler. I only read [this introductory blog post](https://reactjs.org/blog/2018/09/10/introducing-the-react-profiler.html), so if this issue is addressed elsewhere I apologize and also request the source to that solution.

Thank you for your time!

**Versions:**
 * `React DevTools 4.0.5`
 * `Firefox: 68.0.2(64-bit)`
 * `Ubuntu: 18.04`

() => {
      const input = inputRef.current;
      if (input !== null && input.files.length > 0) {
        const fileReader = new FileReader();
        fileReader.addEventListener('load', () => {
          try {
            const raw = ((fileReader.result: any): string);
            const profilingDataExport = ((JSON.parse(
              raw,
            ): any): ProfilingDataExport);
            profilerStore.profilingData = prepareProfilingDataFrontendFromExport(
              profilingDataExport,
            );
          } catch (error) {
            modalDialogDispatch({
              type: 'SHOW',
              title: 'Import failed',
              content: (
                <Fragment>
                  <div>The profiling data you selected cannot be imported.</div>
                  {error !== null && (
                    <div className={styles.ErrorMessage}>{error.message}</div>
                  )}
                </Fragment>
              ),
            });
          }
        });
        
        fileReader.readAsText(input.files[0]);