Offer User Timing in workers

LayoutTests/http/tests/workers/resources/performance-timeline-worker.js

Index: LayoutTests/http/tests/workers/resources/performance-timeline-worker.js
diff --git a/LayoutTests/http/tests/workers/resources/performance-timeline-worker.js b/LayoutTests/http/tests/workers/resources/performance-timeline-worker.js
new file mode 100644
index 0000000000000000000000000000000000000000..97cc588c7d19d9a35476e3671208b10e092472de
--- /dev/null
+++ b/LayoutTests/http/tests/workers/resources/performance-timeline-worker.js
@@ -0,0 +1,31 @@
+importScripts('../../resources/testharness.js');
+
+promise_test(function(test) {
+    var durationMsec = 100;
+
+    return new Promise(function(resolve) {
+        performance.mark('startMark');
+        setTimeout(resolve, durationMsec);
+      }).then(function() {
+          performance.mark('endMark');
+          performance.measure('measure', 'startMark', 'endMark');
+
+          var startMark = performance.getEntriesByName('startMark')[0];
+          var endMark = performance.getEntriesByName('endMark')[0];
+          var measure = performance.getEntriesByType('measure')[0];
+
+          assert_equals(measure.startTime, startMark.startTime);
+          assert_approx_equals(endMark.startTime - startMark.startTime,
+                               measure.duration, 0.001);
+          assert_greater_than(measure.duration, durationMsec);
+
+          assert_equals(performance.getEntriesByType('mark').length, 2);
+          assert_equals(performance.getEntriesByType('measure').length, 1);
+          performance.clearMarks('startMark');
+          performance.clearMeasures('measure');
+          assert_equals(performance.getEntriesByType('mark').length, 1);
+          assert_equals(performance.getEntriesByType('measure').length, 0);
+      });
+  }, 'User Timing');
+
+done();