"DevTools failed to load SourceMap" trying to run Dart Web example

[Guyren Howe]

I'm trying to run the Dart Web example on my Mac running the latest Catalina. I copy-pasted the code from the Dart website, did webdev serve, and then when I look in the console in the latest Chrome on my Mac, I get:

DevTools failed to load SourceMap: Could not load content for http://localhost:8080/packages/build_web_compilers/src/dev_compiler_stack_trace/stack_trace_mapper.dart.js.map: HTTP error: status code 404, net::ERR_HTTP_RESPONSE_CODE_FAILURE

I've disabled AdBlock. I can see in the Network tab of the chrome debugger that it loads all manner of other things successfully.