Invalid argument error when connecting to Google apps using the internal toolchain

Devtools is crashing when connecting to internal Google apps.

The error is like:
```
FormatException: Unexpected character (at character 1)
Invalid argument (must be a file:// URI String)
```

See b/359067065 for details of this.

Start by reproducing the connection to an internal Google app and inspect the URI passed to the internal toolchain; use b/359067065 for the reported details. Done means the connection no longer crashes with FormatException and handles the required file:// URI.

Written by the indexing model from the issue text.