Add startTime to metrics

A metric startTime makes possible to order events by time reported.

Change-Id: I1a404192dbf989e1762846cdaa22a5c1adffff8c

polygerrit-ui/app/elements/core/gr-reporting/gr-reporting.js

@@ -184,7 +184,7 @@
     },
 
     now() {
-      return window.performance.now();
+      return Math.round(window.performance.now());
     },
 
     _arePluginsLoaded() {
@@ -205,6 +205,7 @@
         detectedExtensions,
         repoName: reportRepoName,
         isInBackgroundTab: document.visibilityState === 'hidden',
+        startTimeMs: this.now(),
       };
       args.splice(4, 0, contextInfo);
       report.apply(this, args);
@@ -238,6 +239,9 @@
       if (contextInfo && contextInfo.isInBackgroundTab !== undefined) {
         detail.inBackgroundTab = contextInfo.isInBackgroundTab;
       }
+      if (contextInfo && contextInfo.startTimeMs) {
+        detail.startTime = contextInfo.startTimeMs;
+      }
       document.dispatchEvent(new CustomEvent(type, {detail}));
       if (opt_noLog) { return; }
       if (type === ERROR.TYPE && category === ERROR.CATEGORY) {
@@ -449,7 +453,7 @@
 
       // Guard against division by zero.
       if (!denominator) { return; }
-      const time = Math.round(this.now() - baseTime);
+      const time = this.now() - baseTime;
       this._reportTiming(averageName, time / denominator);
     },
 
@@ -459,8 +463,7 @@
      * @param {number} time The time to report as an integer of milliseconds.
      */
     _reportTiming(name, time) {
-      this.reporter(TIMING.TYPE, TIMING.CATEGORY_UI_LATENCY, name,
+      this.reporter(TIMING.TYPE, TIMING.CATEGORY_UI_LATENCY, name, time);
-          Math.round(time));
     },
 
     /**

polygerrit-ui/app/elements/core/gr-reporting/gr-reporting_test.html

@@ -160,14 +160,14 @@ limitations under the License.
     test('time and timeEnd', () => {
       const nowStub = sandbox.stub(element, 'now').returns(0);
       element.time('foo');
-      nowStub.returns(1.1);
+      nowStub.returns(1);
       element.time('bar');
       nowStub.returns(2);
       element.timeEnd('bar');
-      nowStub.returns(3.511);
+      nowStub.returns(3);
       element.timeEnd('foo');
       assert.isTrue(element.reporter.calledWithExactly(
-          'timing-report', 'UI Latency', 'foo', 4
+          'timing-report', 'UI Latency', 'foo', 3
       ));
       assert.isTrue(element.reporter.calledWithExactly(
           'timing-report', 'UI Latency', 'bar', 1
@@ -249,6 +249,21 @@ limitations under the License.
       ));
     });
 
+    test('report start time', () => {
+      element.reporter.restore();
+      sandbox.stub(element, 'now').returns(42);
+      sandbox.spy(element, 'defaultReporter');
+      const dispatchStub = sandbox.spy(document, 'dispatchEvent');
+      element.pluginsLoaded();
+      element.time('timeAction');
+      element.timeEnd('timeAction');
+      assert.isTrue(element.defaultReporter.getCall(2).calledWithMatch(
+          'timing-report', 'UI Latency', 'timeAction', 0,
+          {startTimeMs: 42}
+      ));
+      assert.equal(dispatchStub.getCall(2).args[0].detail.startTime, 42);
+    });
+
     suite('plugins', () => {
       setup(() => {
         element.reporter.restore();