Import //fetch from Web Platform Tests.

third_party/WebKit/LayoutTests/external/wpt/fetch/api/basic/accept-header.js

+if (this.document === undefined) {
+  importScripts("/resources/testharness.js");
+  importScripts("../resources/utils.js");
+}
+
+promise_test(function() {
+  return fetch(RESOURCES_DIR + "inspect-headers.py?headers=Accept").then(function(response) {
+    assert_equals(response.status, 200, "HTTP status is 200");
+    assert_equals(response.type , "basic", "Response's type is basic");
+    assert_equals(response.headers.get("x-request-accept"), "*/*", "Request has accept header with value '*/*'");
+  });
+}, "Request through fetch should have 'accept' header with value '*/*'");
+
+promise_test(function() {
+  return fetch(RESOURCES_DIR + "inspect-headers.py?headers=Accept", {"headers": [["Accept", "custom/*"]]}).then(function(response) {
+    assert_equals(response.status, 200, "HTTP status is 200");
+    assert_equals(response.type , "basic", "Response's type is basic");
+    assert_equals(response.headers.get("x-request-accept"), "custom/*", "Request has accept header with value 'custom/*'");
+  });
+}, "Request through fetch should have 'accept' header with value 'custom/*'");
+
+promise_test(function() {
+  return fetch(RESOURCES_DIR + "inspect-headers.py?headers=Accept-Language").then(function(response) {
+    assert_equals(response.status, 200, "HTTP status is 200");
+    assert_equals(response.type , "basic", "Response's type is basic");
+    assert_true(response.headers.has("x-request-accept-language"));
+  });
+}, "Request through fetch should have a 'accept-language' header");
+
+promise_test(function() {
+  return fetch(RESOURCES_DIR + "inspect-headers.py?headers=Accept-Language", {"headers": [["Accept-Language", "bzh"]]}).then(function(response) {
+    assert_equals(response.status, 200, "HTTP status is 200");
+    assert_equals(response.type , "basic", "Response's type is basic");
+    assert_equals(response.headers.get("x-request-accept-language"), "bzh", "Request has accept header with value 'bzh'");
+  });
+}, "Request through fetch should have 'accept-language' header with value 'bzh'");
+
+done();