Import //fetch from Web Platform Tests.

third_party/WebKit/LayoutTests/external/wpt/fetch/api/basic/mode-same-origin.js

+if (this.document === undefined) {
+  importScripts("/resources/testharness.js");
+  importScripts("../resources/utils.js");
+  importScripts("/common/get-host-info.sub.js")
+}
+
+function fetchSameOrigin(url, shouldPass) {
+  promise_test(function(test) {
+    if (shouldPass)
+      return fetch(url , {"mode": "same-origin"}).then(function(resp) {
+        assert_equals(resp.status, 200, "HTTP status is 200");
+        assert_equals(resp.type, "basic", "response type is basic");
+      });
+    else
+      return promise_rejects(test, new TypeError, fetch(url, {mode: "same-origin"}));
+  }, "Fetch "+ url + " with same-origin mode");
+}
+
+var host_info = get_host_info();
+
+fetchSameOrigin(RESOURCES_DIR + "top.txt", true);
+fetchSameOrigin(host_info.HTTP_ORIGIN + "/fetch/api/resources/top.txt", true);
+fetchSameOrigin(host_info.HTTPS_ORIGIN + "/fetch/api/resources/top.txt", false);
+fetchSameOrigin(host_info.HTTP_REMOTE_ORIGIN + "/fetch/api/resources/top.txt", false);
+
+var redirPath = dirname(location.pathname) + RESOURCES_DIR + "redirect.py?location=";
+
+fetchSameOrigin(redirPath + RESOURCES_DIR + "top.txt", true);
+fetchSameOrigin(redirPath + host_info.HTTP_ORIGIN + "/fetch/api/resources/top.txt", true);
+fetchSameOrigin(redirPath + host_info.HTTPS_ORIGIN + "/fetch/api/resources/top.txt", false);
+fetchSameOrigin(redirPath + host_info.HTTP_REMOTE_ORIGIN + "/fetch/api/resources/top.txt", false);
+
+done();
+