file_server: Chrome DevTools Workspaces stopped working

[fonsp]

Describe the bug

The Chrome DevTools Workspaces feature, which allows editing local source files directly from the inspector (💕), stopped working in combination with a local file_server. I bisected the problem, and it appeared between v0.102.0 and v0.103.0, which leads to #1028.

Indeed, this SO answer suggests that the Workspaces feature looks at the date headers in the response, and those were added in #1028.

Steps to Reproduce

Serve a basic static site with file_server, visit the site in chrome and follow these steps to set up Workspaces.

Environment

Here is a screenshot of the headers of a (recently edited) file, next to my local time, which is GMT+2. It looks correct.

• OS: MacOS 12
• deno version: 1.19.2
• std version: Working on v0.87.0 until v0.102.0, broken on v0.103.0 until v0.140.0.