Fix as=fetch preload where preload is used before response arrives

[1] broke link rel="preload" as="fetch" handling for the case where
 - It's attached with XHR (not fetch()), and
 - The response body arrives after matching.

1: https://crrev.com/740fabd5a1a6868121315649aa760007c88a180f

Bug: 894819
Change-Id: I8d15639a4f63f41bc3ee1e0a704e1fb6510f7f56
Reviewed-on: https://chromium-review.googlesource.com/c/1476875Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Kinuko Yasuda <kinuko@chromium.org>
Auto-Submit: Yutaka Hirano <yhirano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#633052}

third_party/blink/renderer/platform/loader/fetch/raw_resource.cc

@@ -271,12 +271,18 @@ void RawResource::ResponseReceived(const ResourceResponse& response) {
 
 void RawResource::ResponseBodyReceived(
     ResponseBodyLoaderDrainableInterface& body_loader) {
+  DCHECK_LE(Clients().size(), 1u);
+  RawResourceClient* client =
+      ResourceClientWalker<RawResourceClient>(Clients()).Next();
   if (IsUnusedPreload()) {
     // For preload, we want to store the body while dispatching
     // onload and onerror events.
     bytes_consumer_for_preload_ = MakeGarbageCollected<BufferingBytesConsumer>(
         &body_loader.DrainAsBytesConsumer());
+    return;
+  }
 
+  if (!client) {
     return;
   }
 
@@ -285,6 +291,14 @@ void RawResource::ResponseBodyReceived(
     // The loading was initiated as a preload (hence UseStreamOnResponse is
     // set), but this resource has been matched with a request without
     // UseStreamOnResponse set.
+    auto* bytes_consumer_for_preload =
+        MakeGarbageCollected<BufferingBytesConsumer>(
+            &body_loader.DrainAsBytesConsumer());
+    auto* bytes_consumer_client =
+        MakeGarbageCollected<PreloadBytesConsumerClient>(
+            *bytes_consumer_for_preload, *this, *client);
+    bytes_consumer_for_preload->SetClient(bytes_consumer_client);
+    bytes_consumer_client->OnStateChange();
     return;
   }
 
@@ -292,12 +306,7 @@ void RawResource::ResponseBodyReceived(
     return;
   }
 
-  BytesConsumer& bytes_consumer = body_loader.DrainAsBytesConsumer();
-  DCHECK_LE(Clients().size(), 1u);
-  ResourceClientWalker<RawResourceClient> w(Clients());
-  while (RawResourceClient* c = w.Next()) {
-    c->ResponseBodyReceived(this, bytes_consumer);
-  }
+  client->ResponseBodyReceived(this, body_loader.DrainAsBytesConsumer());
 }
 
 CachedMetadataHandler* RawResource::CreateCachedMetadataHandler(

third_party/blink/web_tests/external/wpt/preload/preload-xhr.html

+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/common/utils.js"></script>
+<script src="/preload/resources/preload_helper.js"></script>
+<script>
+
+const dummyContent = '<?xml version="1.0" encoding="utf-8"?>\n<root>Text.me</root>\n';
+promise_test(async (t) => {
+  const url = `resources/dummy.xml?token=${token()}`;
+  const link = document.createElement('link');
+  link.rel = 'preload';
+  link.as = 'fetch';
+  link.href = url;
+  link.crossOrigin = 'anonymous';
+
+  document.head.appendChild(link);
+
+  const xhr = new XMLHttpRequest();
+  await new Promise((resolve, reject) => {
+    xhr.onloadend = resolve;
+    xhr.onloaderror = reject;
+    xhr.open('GET', url);
+    xhr.send();
+  });
+  verifyNumberOfResourceTimingEntries(url, 1);
+  assert_equals(xhr.status, 200);
+  assert_equals(xhr.responseText, dummyContent);
+
+}, 'Make an XHR request immediately after creating link rel=preload.');
+
+promise_test(async (t) => {
+  const url = `resources/dummy.xml?token=${token()}`;
+  const link = document.createElement('link');
+  link.rel = 'preload';
+  link.as = 'fetch';
+  link.href = url;
+  link.crossOrigin = 'anonymous';
+
+  await new Promise((resolve, reject) => {
+    link.addEventListener('load', resolve, {once: true});
+    link.addEventListener('error', reject, {once: true});
+    document.head.appendChild(link);
+  });
+
+  const xhr = new XMLHttpRequest();
+  await new Promise((resolve, reject) => {
+    xhr.onloadend = resolve;
+    xhr.onloaderror = reject;
+    xhr.open('GET', url);
+    xhr.send();
+  });
+  verifyNumberOfResourceTimingEntries(url, 1);
+  assert_equals(xhr.status, 200);
+  assert_equals(xhr.responseText, dummyContent);
+}, 'Make an XHR request after loading link rel=preload.');
+
+</script>