[fetch-later] Promote fetch-later wpt tests and fix some flakiness

fetch/fetch-later/quota/same-origin-iframe/multiple-iframes.tentative.https.window.js → fetch/fetch-later/quota/same-origin-iframe/multiple-iframes.https.window.js

@@ -48,15 +48,15 @@ promise_test(async _ => {
   // Queues a max bytes request in the root document, which should also be
   // rejected, because the target URL's origin `HTTPS_ORIGIN` already has 64kb
   // pending from 1st request.
-  assert_throws_dom(
-      'QuotaExceededError',
+  assert_throws_quotaexceedederror(
       () => fetchLater(requestUrl, {
         method: 'POST',
         body: generatePayload(
             getRemainingQuota(QUOTA_PER_ORIGIN, requestUrl, headers), dataType),
         // Required, as the size of referrer also take up quota.
         referrer: '',
-      }));
+      }),
+      null, null);
 
   // Release quota taken by the pending requests for subsequent tests.
   for (const element of document.querySelectorAll('iframe')) {

fetch/fetch-later/resources/fetch-later-helper.js

@@ -399,8 +399,7 @@ class FetchLaterIframeExpectation {
             url, 'nothing', this.expectedErrorType.name);
       }
       if (e.data.type === FetchLaterIframeMessageType.ERROR) {
-        if (e.data.error.constructor === this.expectedErrorType &&
-            e.data.error.name === this.expectedErrorType.name) {
+        if (e.data.error.name === this.expectedErrorType.name) {
           return true;
         }
         throw new FetchLaterExpectationError(
@@ -417,9 +416,7 @@ class FetchLaterIframeExpectation {
         const actual = e.data.error.name || e.data.error.type;
         if (this.expectedDomErrorName === 'QuotaExceededError') {
           return actual == this.expectedDomErrorName;
-        } else if (
-            e.data.error.constructor.name === 'DOMException' &&
-            actual == this.expectedDomErrorName) {
+        } else if (actual == this.expectedDomErrorName) {
           return true;
         }
         throw new FetchLaterExpectationError(

fetch/fetch-later/resources/fetch-later.html

@@ -30,7 +30,11 @@
       fetchLater(TARGET_URL, REQUEST_INIT);
       postMessageBack({type: FetchLaterIframeMessageType.DONE});
     } catch (e) {
-      postMessageBack({type: FetchLaterIframeMessageType.ERROR, error: e});
+      postMessageBack({
+        type: FetchLaterIframeMessageType.ERROR,
+        // When an error is caught, it might not be cloneable across the boundary.
+        error: {name: e.name, message: e.message}
+      });
     }
   </script>
 </body>