Allow co-existing entrypTypes and buffered options in PerformanceObse…

…rver.observe() method.

It's allowed, but the buffered option is ignored. This is what Blink
does [1], what WebKit does [2]. (Both code blocks are inside the else
branch of if `has entryTypes`)

The web-platform-test in this change was originally copied from
buffered-flag-after-timeout.any.js and modified.

[1] https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/timing/performance_observer.cc;l=264-273;drc=78780a188fe3c79fe815b170f4ea33e62ceb6e04
[2] https://searchfox.org/wubkat/rev/6c800745251d53d6486443d63b35828504446c5d/Source/WebCore/page/PerformanceObserver.cpp#90-100
[3] https://searchfox.org/mozilla-central/rev/e24277e20c492b4a785b4488af02cca062ec7c2c/testing/web-platform/tests/performance-timeline/buffered-flag-after-timeout.any.js

Differential Revision: https://phabricator.services.mozilla.com/D233447

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1915589
gecko-commit: fb9d78b726556ac65a13e937410fe92f159b203f
gecko-reviewers: sefeng

performance-timeline/buffered-flag-with-entryTypes-observer.tentative.any.js

@@ -0,0 +1,13 @@
+async_test(t => {
+  performance.mark('foo');
+  // Use a timeout to ensure the remainder of the test runs after the entry is created.
+  t.step_timeout(() => {
+    // `buffered` flag set to true but with entryTypes so that
+    // the `buffered` flag should be ignored, thus there should be no entry.
+    new PerformanceObserver(() => {
+      assert_unreached('Should not have observed any entry!');
+    }).observe({entryTypes: ['mark'], buffered: true});
+    // Use a timeout to give time to the observer.
+    t.step_timeout(t.step_func_done(() => {}), 100);
+  }, 0);
+}, 'PerformanceObserver without buffered flag set to false cannot see past entries.');