library-reference-1.ts fails with runtests-browser

[ghost]

gulp runtests-browser --browser chrome --test library-reference-1.ts breaks.
From the local library-reference-1.trace.json:

[
    "======== Resolving type reference directive 'jquery', containing file '//src/consumer.ts', root directory 'types'. ========",
    "Resolving with primary search path 'types'",
    "File 'types/jquery/package.json' does not exist.",
    "File 'types/jquery/index.d.ts' does not exist.",
    "Looking up in 'node_modules' folder, initial location '//src/'",
    "File '//src/node_modules/jquery.ts' does not exist.",
    "File '//src/node_modules/jquery.d.ts' does not exist.",
    "File '//src/node_modules/jquery/package.json' does not exist.",
    "File '//src/node_modules/jquery/index.ts' does not exist.",
    "File '//src/node_modules/jquery/index.d.ts' does not exist.",
    "File '//src/node_modules/@types/jquery.ts' does not exist.",
    "File '//src/node_modules/@types/jquery.d.ts' does not exist.",
    "File '//src/node_modules/@types/jquery/package.json' does not exist.",
    "File '//src/node_modules/@types/jquery/index.ts' does not exist.",
    "File '//src/node_modules/@types/jquery/index.d.ts' does not exist.",
    "======== Type reference directive 'jquery' was not resolved. ========"
]

The correct trace should be:

[
    "======== Resolving type reference directive 'jquery', containing file '/src/consumer.ts', root directory 'types'. ========",
    "Resolving with primary search path 'types'",
    "File 'types/jquery/package.json' does not exist.",
    "File 'types/jquery/index.d.ts' exist - use it as a name resolution result.",
    "======== Type reference directive 'jquery' was successfully resolved to 'types/jquery/index.d.ts', primary: true. ========",
    "======== Resolving type reference directive 'jquery', containing file '/src/__inferred type names__.ts', root directory 'types'. ========",
    "Resolving with primary search path 'types'",
    "File 'types/jquery/package.json' does not exist.",
    "File 'types/jquery/index.d.ts' exist - use it as a name resolution result.",
    "======== Type reference directive 'jquery' was successfully resolved to 'types/jquery/index.d.ts', primary: true. ========"
]

Since // @filename: /src/types/jquery/index.d.ts is explicitly declared to exist in the test,
there must be some error in the mock file system when run in the browser.

[ghost]

Looking at the console it looks like we are getting 500 (Internal Server Error) for tests/baselines/local/library-reference-1.errors.txt, tests/baselines/library-reference-1.errors.txt, tests/baselines/local/library-reference-1.trace.json, and tests/baselines/local/library-reference-1.js. Not sure how this is related to the problem though.
EDIT: Upon further inspection it looks like webTestServer.ts is intentionally giving "500" errors for for files that haven't been found. We should probably use 404 instead.