Fetch: Enable BufferingBytesConsumerDelay by default.

This CL also fixes a content_browsertest test case that assumed the
fetch response body would be immediately drained.

Bug: 954442
Change-Id: I22c41758150f427072f18c3ac79a82a1f9678f28
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1736868Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Ben Kelly <wanderview@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684083}

content/test/data/stale-while-revalidate.html

@@ -10,8 +10,8 @@ function wait25ms() {
 // runTest() will be called by the browser test.
 async function runTest() {
   const url = 'stale-script.js';
-  const response = await fetch(url);
-  const response2 = await fetch(url);
+  const response = await fetch(url).then(r => r.text());
+  const response2 = await fetch(url).then(r => r.text());
   while(true) {
     const revalidation_check = await fetch('stale-script.js');
     if (performance.getEntriesByName(new URL(url, document.location)).length == 2) {

third_party/blink/common/features.cc

@@ -379,7 +379,7 @@ const base::Feature kBlinkHeapUnifiedGCScheduling{
 // Enables a delay before BufferingBytesConsumer begins reading from its
 // underlying consumer when instantiated with CreateWithDelay().
 const base::Feature kBufferingBytesConsumerDelay{
-    "BufferingBytesConsumerDelay", base::FEATURE_DISABLED_BY_DEFAULT};
+    "BufferingBytesConsumerDelay", base::FEATURE_ENABLED_BY_DEFAULT};
 const base::FeatureParam<int> kBufferingBytesConsumerDelayMilliseconds{
     &kBufferingBytesConsumerDelay, "milliseconds", 50};