`Request`'s `Headers` fails to be constructed with an array or an object

[jeenalee]

From tests/wpt/web-platform-tests/fetch/api/request/request-headers.html, following test fails:

test(function() {
  var array = [["hello", "worldAHH"]];
  var object = {"hello": 'worldOOH'};
  var headers = new Headers(array);

  assert_equals(headers.get("hello"), "worldAHH");

  var request1 = new Request("", {"headers": headers});
  var request2 = new Request("", {"headers": array});
  var request3 = new Request("", {"headers": object});

  assert_equals(request1.headers.get("hello"), "worldAHH");
  assert_equals(request2.headers.get("hello"), "worldAHH");
  assert_equals(request3.headers.get("hello"), "worldOOH");
}, "Testing request header creations with various objects");

request1 is constructed with the expected headers. request2 and request3 get constructed, but the headers remain empty. This is (probably) somewhat related to the other failing test in the same file:

promise_test(function(test) {
  var request = new Request("", {"headers" : [["Content-Type", ""]], "body" : "this is my plate", "method" : "POST"});
  return request.blob().then(function(blob) {
    assert_equals(blob.type, "", "Blob type should be the empty string");
  });
}, "Testing empty Request Content-Type header");