Import //fetch from Web Platform Tests.

third_party/WebKit/LayoutTests/external/wpt/fetch/api/credentials/cookies.js

+if (this.document === undefined) {
+  importScripts("/resources/testharness.js");
+  importScripts("../resources/utils.js");
+}
+
+function cookies(desc, credentials1, credentials2 ,cookies) {
+  var url = RESOURCES_DIR + "top.txt"
+  var urlParameters = "";
+  var urlCleanParameters = "";
+  if (cookies) {
+    urlParameters +="?pipe=header(Set-Cookie,";
+    urlParameters += cookies.join(",True)|header(Set-Cookie,") +  ",True)";
+    urlCleanParameters +="?pipe=header(Set-Cookie,";
+    urlCleanParameters +=  cookies.join("%3B%20max-age=0,True)|header(Set-Cookie,") +  "%3B%20max-age=0,True)";
+  }
+
+  var requestInit = {"credentials": credentials1}
+  promise_test(function(test){
+    var requestInit = {"credentials": credentials1}
+    return fetch(url + urlParameters, requestInit).then(function(resp) {
+      assert_equals(resp.status, 200, "HTTP status is 200");
+      assert_equals(resp.type , "basic", "Response's type is basic");
+      //check cookies sent
+      return fetch(RESOURCES_DIR + "inspect-headers.py?headers=cookie" , {"credentials": credentials2});
+    }).then(function(resp) {
+      assert_equals(resp.status, 200, "HTTP status is 200");
+      assert_equals(resp.type , "basic", "Response's type is basic");
+      assert_false(resp.headers.has("Cookie") , "Cookie header is not exposed in response");
+      if (credentials1 != "omit" && credentials2 != "omit") {
+        assert_equals(resp.headers.get("x-request-cookie") , cookies.join("; "), "Request include cookie(s)");
+      }
+      else {
+        assert_false(resp.headers.has("x-request-cookie") , "Request does not have cookie(s)");
+      }
+      //clean cookies
+      return fetch(url + urlCleanParameters, {"credentials": "include"});
+    }).catch(function(e) {
+      return fetch(url + urlCleanParameters, {"credentials": "include"}).then(function() {
+         return Promise.reject(e);
+      });
+    });
+  }, desc);
+}
+
+cookies("Include mode: 1 cookie", "include", "include", ["a=1"]);
+cookies("Include mode: 2 cookies", "include", "include", ["b=2", "c=3"]);
+cookies("Omit mode: discard cookies", "omit", "omit", ["d=4"]);
+cookies("Omit mode: no cookie is stored", "omit", "include", ["e=5"]);
+cookies("Omit mode: no cookie is sent", "include", "omit", ["f=6"]);
+cookies("Same-origin mode: 1 cookie", "same-origin", "same-origin", ["a=1"]);
+cookies("Same-origin mode: 2 cookies", "same-origin", "same-origin", ["b=2", "c=3"]);
+
+done();