[Stream] Notify ReadObserver of Stream abortion

third_party/WebKit/LayoutTests/http/tests/serviceworker/resources/respond-with-response-body-with-invalid-chunk-worker.js

+self.addEventListener('fetch', event => {
+    if (!event.request.url.match(/body-stream-with-invalid-chunk$/))
+      return;
+    const stream = new ReadableStream({start: controller => {
+        // The argument is intentionally a string, not a Uint8Array.
+        controller.enqueue('hello');
+      }});
+    const headers = { 'x-content-type-options': 'nosniff' };
+    event.respondWith(new Response(stream, { headers }));
+  });