HAR file downloaded from DevTools can not be loaded in Chrome DevTools

[elliette]

Steps to reproduce:

1. Connect to an app that makes network requests
2. Navigate to network screen
3. Choose option to download as HAR file
4. Open Chrome DevTools
5. Navigate to Chrome DevTools network tab
6. Import the dowloaded HAR file

Import fails with the following error:

Failed to load HAR file with following error: Casting to number results in NaN

Potentially we are creating an invalid HAR file?