[EventTiming] More flakiness fixes

This CL applies fixes similar to a previous: we do not assume that the
first callback to the PerformanceObserver will include the mousedown
entry and instead abort and wait until a further callback which does
include it.

Bug: 1074048
Change-Id: Ifdf01b0abae025fa67f3ff355324d4b6204111a8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2204618
Auto-Submit: Nicolás Peña Moreno <npm@chromium.org>
Commit-Queue: Yoav Weiss <yoavweiss@chromium.org>
Reviewed-by: Yoav Weiss <yoavweiss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#769577}

third_party/blink/web_tests/external/wpt/event-timing/buffered-and-duration-threshold.html

@@ -24,6 +24,8 @@ promise_test(async t => {
     const afterFirstClick = performance.now();
     new PerformanceObserver(t.step_func(list => {
       const mouseDowns = list.getEntriesByName('mousedown');
+      if (mouseDowns.length === 0)
+        return;
       assert_equals(mouseDowns.length, 1, 'Should only observe 1 click!');
       assert_greater_than(mouseDowns[0].processingStart, afterFirstClick,
         'The entry should not be the first click!!');

third_party/blink/web_tests/external/wpt/event-timing/disconnect-target.html

@@ -15,6 +15,8 @@ async_test(function(t) {
   assert_implements(window.PerformanceEventTiming, 'Event Timing is not supported.');
   const observer = new PerformanceObserver(t.step_func_done((entryList) => {
     const entries = entryList.getEntries().filter(e => e.name === 'mousedown');
+    if (entries.length === 0)
+      return;
     // There must only be one click entry.
     assert_equals(entries.length, 1);
     const entry = entries[0];

third_party/blink/web_tests/external/wpt/event-timing/resources/crossiframe-childframe.html

@@ -8,7 +8,10 @@
   const clickTimeMin = performance.now();
   const observerPromise = new Promise(resolve => {
     new PerformanceObserver(entryList => {
-      resolve(entryList.getEntries().filter(entry => entry.name === 'mousedown'));
+      const mouseDowns = entryList.getEntriesByName('mousedown');
+      if (mouseDowns.length === 0)
+        return;
+      resolve(mouseDowns);
     }).observe({ type:'event' });
   });
   const entries = await observerPromise;

third_party/blink/web_tests/external/wpt/event-timing/retrievability.html

@@ -32,7 +32,7 @@
   async_test(function(t) {
     assert_implements(window.PerformanceEventTiming, 'Event Timing is not supported.');
     new PerformanceObserver(t.step_func(entryList => {
-      if (entryList.getEntriesByName('mousedown')) {
+      if (entryList.getEntriesByName('mousedown').length > 0) {
         validateEntries();
         t.done();
       }