Import //fetch from Web Platform Tests.

third_party/WebKit/LayoutTests/external/wpt/fetch/api/cors/cors-preflight.js

+if (this.document === undefined) {
+  importScripts("/resources/testharness.js");
+  importScripts("/common/utils.js");
+  importScripts("../resources/utils.js");
+  importScripts("/common/get-host-info.sub.js");
+}
+
+function headerNames(headers)
+{
+    let names = [];
+    for (let header of headers)
+        names.push(header[0].toLowerCase());
+    return names
+}
+
+/*
+  Check preflight is done
+  Control if server allows method and headers and check accordingly
+  Check control access headers added by UA (for method and headers)
+*/
+function corsPreflight(desc, corsUrl, method, allowed, headers, safeHeaders) {
+  return promise_test(function(test) {
+    var uuid_token = token();
+    return fetch(RESOURCES_DIR + "clean-stash.py?token=" + uuid_token).then(function(response) {
+      var url = corsUrl;
+      var urlParameters = "?token=" + uuid_token + "&max_age=0";
+      var requestInit = {"mode": "cors", "method": method};
+      var requestHeaders = [];
+      if (headers)
+        requestHeaders.push.apply(requestHeaders, headers);
+      if (safeHeaders)
+        requestHeaders.push.apply(requestHeaders, safeHeaders);
+      requestInit["headers"] = requestHeaders;
+
+      if (allowed) {
+        urlParameters += "&allow_methods=" + method + "&control_request_headers";
+        if (headers) {
+          //Make the server allow the headers
+          urlParameters += "&allow_headers=" + headerNames(headers).join("%20%2C");
+        }
+        return fetch(url + urlParameters, requestInit).then(function(resp) {
+          assert_equals(resp.status, 200, "Response's status is 200");
+          assert_equals(resp.headers.get("x-did-preflight"), "1", "Preflight request has been made");
+          if (headers) {
+            var actualHeaders = resp.headers.get("x-control-request-headers").toLowerCase().split(",");
+            for (var i in actualHeaders)
+              actualHeaders[i] = actualHeaders[i].trim();
+            for (var header of headers)
+              assert_in_array(header[0].toLowerCase(), actualHeaders, "Preflight asked permission for header: " + header);
+
+            let accessControlAllowHeaders = headerNames(headers).sort().join(",");
+            assert_equals(resp.headers.get("x-control-request-headers"), accessControlAllowHeaders, "Access-Control-Allow-Headers value");
+            return fetch(RESOURCES_DIR + "clean-stash.py?token=" + uuid_token);
+          } else {
+            assert_equals(resp.headers.get("x-control-request-headers"), null, "Access-Control-Request-Headers should be omitted")
+          }
+        });
+      } else {
+        return promise_rejects(test, new TypeError(), fetch(url + urlParameters, requestInit)).then(function(){
+          return fetch(RESOURCES_DIR + "clean-stash.py?token=" + uuid_token);
+        });
+      }
+    });
+  }, desc);
+}
+
+var corsUrl = get_host_info().HTTP_REMOTE_ORIGIN + dirname(location.pathname) + RESOURCES_DIR + "preflight.py";
+
+corsPreflight("CORS [DELETE], server allows", corsUrl, "DELETE", true);
+corsPreflight("CORS [DELETE], server refuses", corsUrl, "DELETE", false);
+corsPreflight("CORS [PUT], server allows", corsUrl, "PUT", true);
+corsPreflight("CORS [PUT], server refuses", corsUrl, "PUT", false);
+corsPreflight("CORS [PATCH], server allows", corsUrl, "PATCH", true);
+corsPreflight("CORS [PATCH], server refuses", corsUrl, "PATCH", false);
+corsPreflight("CORS [NEW], server allows", corsUrl, "NEW", true);
+corsPreflight("CORS [NEW], server refuses", corsUrl, "NEW", false);
+
+corsPreflight("CORS [GET] [x-test-header: allowed], server allows", corsUrl, "GET", true, [["x-test-header1", "allowed"]]);
+corsPreflight("CORS [GET] [x-test-header: refused], server refuses", corsUrl, "GET", false, [["x-test-header1", "refused"]]);
+
+var headers = [
+    ["x-test-header1", "allowedOrRefused"],
+    ["x-test-header2", "allowedOrRefused"],
+    ["X-test-header3", "allowedOrRefused"],
+    ["x-test-header-b", "allowedOrRefused"],
+    ["x-test-header-D", "allowedOrRefused"],
+    ["x-test-header-C", "allowedOrRefused"],
+    ["x-test-header-a", "allowedOrRefused"],
+    ["Content-Type", "allowedOrRefused"],
+];
+var safeHeaders= [
+    ["Accept", "*"],
+    ["Accept-Language", "bzh"],
+    ["Content-Language", "eu"],
+];
+
+corsPreflight("CORS [GET] [several headers], server allows", corsUrl, "GET", true, headers, safeHeaders);
+corsPreflight("CORS [GET] [several headers], server refuses", corsUrl, "GET", false, headers, safeHeaders);
+corsPreflight("CORS [PUT] [several headers], server allows", corsUrl, "PUT", true, headers, safeHeaders);
+corsPreflight("CORS [PUT] [several headers], server refuses", corsUrl, "PUT", false, headers, safeHeaders);
+
+corsPreflight("CORS [PUT] [only safe headers], server allows", corsUrl, "PUT", true, null, safeHeaders);
+
+done();