My feeling is that for multiple distinct headers that conflict, we should generally go with the first (When we can't just fail the request), as at least a partial mitigation against response-splitting attacks.  While that logic doesn't really apply to semi-colon delimited lists, it would be consistent to prefer the first, so I think this is a reasonable direction to go in.

The issue seems to be out of TE-scope as it is related to MIME type parameters. Hence, adding label TE-NeedsTriageHelp for further investigation from dev team.

Thanks...!!

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5518c1a563526f51674feb28bfedd527e1c94072

commit 5518c1a563526f51674feb28bfedd527e1c94072
Author: Matt Menke <mmenke@chromium.org>
Date: Fri Oct 05 22:03:19 2018

Content-Type parser: Update to more closely match latest WHATWG spec.

The latest spec can be found at https://mimesniff.spec.whatwg.org/

In particular, this CL makes the parser:
* Trim whitespace within quotes.
* Not ignore first "(" in a charset or anything after it.
* Allow quoted empty strings.
* Prefer values closed to the beginning of the string.

This makes a number of previously failing WPT layout tests pass,
though there still remain some deviations from the spec:
* When there are multiple Content-Type lines, we use the last.
* We don't restrict the characters we allow in Content-Type fields.
* We trim whitespace before the first quote characters (The spec
  indicates that if there's a space after the "=", it's treated as a
  non-quoted string).

Bug:  788491 ,  772343 
Change-Id: Ieeb11eb76d824a9df5130d8c5dc0be3b442ca366
Reviewed-on: https://chromium-review.googlesource.com/c/1257443
Commit-Queue: Matt Menke <mmenke@chromium.org>
Reviewed-by: Asanka Herath <asanka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597331}
[modify] https://crrev.com/5518c1a563526f51674feb28bfedd527e1c94072/net/http/http_response_headers_unittest.cc
[modify] https://crrev.com/5518c1a563526f51674feb28bfedd527e1c94072/net/http/http_util.cc
[modify] https://crrev.com/5518c1a563526f51674feb28bfedd527e1c94072/net/http/http_util_unittest.cc
[modify] https://crrev.com/5518c1a563526f51674feb28bfedd527e1c94072/third_party/WebKit/LayoutTests/external/wpt/mimesniff/mime-types/charset-parameter.window-expected.txt