fix(benchpress): support nested intervals

Chrome sometimes reports nested `FunctionCall` intervals in the timeline,
which should be ignored for measuring the `script` metric.

Might solve #2116

modules/benchpress/src/metric/perflog_metric.ts

@@ -168,7 +168,8 @@ export class PerflogMetric extends Metric {
     var gcTimeInScript = 0;
     var renderTimeInScript = 0;
 
-    var intervalStarts = {};
+    var intervalStarts: StringMap<string, any> = {};
+    var intervalStartCount: StringMap<string, number> = {};
     events.forEach((event) => {
       var ph = event['ph'];
       var name = event['name'];
@@ -187,9 +188,16 @@ export class PerflogMetric extends Metric {
       if (isPresent(markStartEvent) && isBlank(markEndEvent) &&
           event['pid'] === markStartEvent['pid']) {
         if (StringWrapper.equals(ph, 'B') || StringWrapper.equals(ph, 'b')) {
+          if (isBlank(intervalStarts[name])) {
+            intervalStartCount[name] = 1;
             intervalStarts[name] = event;
+          } else {
+            intervalStartCount[name]++;
+          }
         } else if ((StringWrapper.equals(ph, 'E') || StringWrapper.equals(ph, 'e')) &&
                    isPresent(intervalStarts[name])) {
+          intervalStartCount[name]--;
+          if (intervalStartCount[name] === 0) {
             var startEvent = intervalStarts[name];
             var duration = (event['ts'] - startEvent['ts']);
             intervalStarts[name] = null;
@@ -217,6 +225,7 @@ export class PerflogMetric extends Metric {
             }
           }
         }
+      }
     });
     result['pureScriptTime'] = result['scriptTime'] - gcTimeInScript - renderTimeInScript;
     return isPresent(markStartEvent) && isPresent(markEndEvent) ? result : null;

modules/benchpress/test/metric/perflog_metric_spec.ts

@@ -343,6 +343,19 @@ export function main() {
                });
          }));
 
+      it('should ignore nested intervals', inject([AsyncTestCompleter], (async) => {
+           aggregate([
+             eventFactory.start('script', 0),
+             eventFactory.start('script', 5),
+             eventFactory.end('script', 10),
+             eventFactory.end('script', 17)
+           ])
+               .then((data) => {
+                 expect(data['scriptTime']).toBe(17);
+                 async.done();
+               });
+         }));
+
       it('should ignore events from different processed as the start mark',
          inject([AsyncTestCompleter], (async) => {
            var otherProcessEventFactory = new TraceEventFactory('timeline', 'pid1');