Do not apply CORB to application/x-www-form-urlencoded.

Bug: 990853, 802836
Change-Id: I7aeba7f34ae3257a8c0d7900a4f266f872273304
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1739646
Commit-Queue: Charlie Reis <creis@chromium.org>
Auto-Submit: Łukasz Anforowicz <lukasza@chromium.org>
Reviewed-by: Charlie Reis <creis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684464}

services/network/cross_origin_read_blocking.cc

@@ -236,7 +236,6 @@ base::flat_set<std::string>& GetNeverSniffedMimeTypes() {
       "application/gzip",
       "application/x-gzip",
       "application/x-protobuf",
-      "application/x-www-form-urlencoded",
       "application/zip",
       // Block multipart responses because a protected type (e.g. JSON) can
       // become multipart if returned in a range request with multiple parts.

services/network/cross_origin_read_blocking_unittest.cc

@@ -2636,7 +2636,6 @@ TEST(CrossOriginReadBlockingTest, GetCanonicalMimeType) {
       {"application/gzip", MimeType::kNeverSniffed},
       {"application/x-protobuf", MimeType::kNeverSniffed},
       {"application/x-gzip", MimeType::kNeverSniffed},
-      {"application/x-www-form-urlencoded", MimeType::kNeverSniffed},
       {"application/zip", MimeType::kNeverSniffed},
       {"multipart/byteranges", MimeType::kNeverSniffed},
       {"text/event-stream", MimeType::kNeverSniffed},

third_party/blink/web_tests/external/wpt/fetch/corb/script-resource-with-nonsniffable-types.tentative.sub.html

@@ -56,7 +56,6 @@ protected_mime_types = [
   "application/gzip",
   "application/x-gzip",
   "application/x-protobuf",
-  "application/x-www-form-urlencoded",
   "application/zip",
   "multipart/byteranges",
   "text/event-stream",