Bug 1547574 [wpt PR 16541] - Web Platform Tests: Append comment with instructions for chrome, a=testonly

Automatic update from web-platform-tests
Web Platform Tests: Append comment with instructions for chrome

The comment, as is today, only describes which flags to pass to
V8 but now how to pass the flag to V8 when launching chrome.
This change adds a little more color and should save developers
time that would have been spent researching how to pass V8 flags
from chrome launch.

Change-Id: I9daa5e6e1089de2dc52248958d0320f03beea83a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1584583
Auto-Submit: Jarryd Goodman <jarrydg@chromium.org>
Reviewed-by: Robert Ma <robertma@chromium.org>
Commit-Queue: Jarryd Goodman <jarrydg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654127}

--

wpt-commits: 61561cd8d8b49e0c5e7019c1f4bd3a9c051050f7
wpt-pr: 16541

testing/web-platform/tests/streams/resources/test-utils.js

@@ -50,6 +50,7 @@ self.constructorThrowsForAll = (constructor, firstArgs) => {
 self.garbageCollect = () => {
   if (self.gc) {
     // Use --expose_gc for V8 (and Node.js)
+    // to pass this flag at chrome launch use: --js-flags="--expose-gc"
     // Exposed in SpiderMonkey shell as well
     self.gc();
   } else if (self.GCController) {