Create resource timing entries for fetch network errors

[noamr]

An initial tests for whatwg/fetch#1215

Added test cases for several network error scenarios. The test cases verify that a resource timing entry is created for those resources, without the "internal" timing info (redirects, networking), as if the resource was cross-origin no-cors and lacked TAO.

The error test cases include:

• CORS fail (which is also covered in existing TAO tests)
• about URLs
• invalid blobs
• Posting to blobs
• Only-if-cached header for a fresh resource
• Abort HTTP/blob request
• Invalid scheme
• Too many redirects
• Invalid certificate
• Host not found
• CSP blocked

These tests come in conjunction with whatwg/fetch#1311

[yoavweiss]

Thanks!! A few comments

[yoavweiss]

LGTM

[noamr]

LGTM

Thanks!
Should probably wait until the spec change is approved and merge at the same time.

[noamr]

Modified test to include only 5 scenarios for now:

• CORS failure
• DNS failure
• Timeout (IP address not found)
• Only-if-cached-resource that wasn't cached
• Too many redirects

Currently Chrome & Firefox are inconsistent around which of these create a resource timing entry.
Safari does not create RT entries for network errors.

[noamr]

This actually catches a Firefox bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1523275

[yoavweiss]

LGTM % nit and suggestion for another test

[noamr]

The Firefox failures are legit, e.g. https://bugzilla.mozilla.org/show_bug.cgi?id=1523275. How does this get merged when it fails firefox nightly?

[noamr]

LGTM % nit and suggestion for another test

Added a test for mixed content.