Issue #1587 - Part 6: Move FetchController/Signal to its own dir

Since it is specced separately from fetch.

dom/abort/tests/worker_fetch_controller.js

@@ -0,0 +1,27 @@
+function testWorkerAbortedFetch() {
+  var fc = new FetchController();
+  fc.abort();
+
+  fetch('slow.sjs', { signal: fc.signal }).then(() => {
+    postMessage(false);
+  }, e => {
+    postMessage(e.name == "AbortError");
+  });
+}
+
+function testWorkerFetchAndAbort() {
+  var fc = new FetchController();
+
+  var p = fetch('slow.sjs', { signal: fc.signal });
+  fc.abort();
+
+  p.then(() => {
+    postMessage(false);
+  }, e => {
+    postMessage(e.name == "AbortError");
+  });
+}
+
+onmessage = function(e) {
+  self[e.data]();
+}