Structured Headers: Include all public tests

This imports all of the tests from the public test repository at
https://github.com/httpwg/structured-header-tests, which have been
automatically converted from JSON to C++ unit tests.

Tests which were already present in structured_headers_unittest.cc
have been removed from that file, to avoid needless redundancy.

Bug: 1069790
Change-Id: I05536c36cb66c7dda43aab2f6c5ae77961120a6a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2146237
Commit-Queue: Ian Clelland <iclelland@chromium.org>
Reviewed-by: Asanka Herath <asanka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#759015}

net/BUILD.gn

@@ -4289,6 +4289,7 @@ test("net_unittests") {
     "http/http_vary_data_unittest.cc",
     "http/mock_allow_http_auth_preferences.cc",
     "http/mock_allow_http_auth_preferences.h",
+    "http/structured_headers_generated_unittest.cc",
     "http/structured_headers_unittest.cc",
     "http/transport_security_persister_unittest.cc",
     "http/transport_security_state_unittest.cc",