What steps will reproduce the problem?
(1) Modify omnibox.js to introduce a typo in one of the Mojo module paths.
(2) Navigate to chrome://omnibox.

What is the expected output?
Some sort of resource loading error indicating which resource failed to load.

What do you see instead?
"Uncaught SyntaxError: Unexpected token <", source:  (1)

The issue is that because WebUI pages have their default resource set to their main HTML page any missing resource instead loads the HTML page. The resulting messages are not helpful in deducing the error.