Speed up the EQT metric computation.

tracing/tracing/metrics/system_health/expected_queueing_time_metric.html

Index: tracing/tracing/metrics/system_health/expected_queueing_time_metric.html
diff --git a/tracing/tracing/metrics/system_health/expected_queueing_time_metric.html b/tracing/tracing/metrics/system_health/expected_queueing_time_metric.html
index 28a4dcb4faaa812bf0ed1e81fed78123f323e731..aa090f65233a4eb6d270cb9518eede966485565a 100644
--- a/tracing/tracing/metrics/system_health/expected_queueing_time_metric.html
+++ b/tracing/tracing/metrics/system_health/expected_queueing_time_metric.html
@@ -93,20 +93,22 @@ tr.exportTo('tr.metrics.sh', function() {
    * Each renderer process adds one sample to the histograms.
    */
   function expectedQueueingTimeMetric(histograms, model) {
-    let chromeHelper = model.getOrCreateHelper(
+    const chromeHelper = model.getOrCreateHelper(
         tr.model.helpers.ChromeModelHelper);
-    let totalHistogram = createHistogramForEQT_(
+    const totalHistogram = createHistogramForEQT_(
         `total:${WINDOW_SIZE_MS}ms_window:renderer_eqt`,
         `The maximum EQT in a ${WINDOW_SIZE_MS}ms sliding window` +
         ' for a given renderer');
-    let interactiveHistogram = createHistogramForEQT_(
+    const interactiveHistogram = createHistogramForEQT_(
         `interactive:${WINDOW_SIZE_MS}ms_window:renderer_eqt`,
         `The maximum EQT in a ${WINDOW_SIZE_MS}ms sliding window` +
         ' for a given renderer while the page is interactive');
-    let rendererHelpers = tr.b.dictionaryValues(chromeHelper.rendererHelpers);
+    const rendererHelpers = tr.b.dictionaryValues(chromeHelper.rendererHelpers);
+    const rendererToInteractiveTimestamps =

[ulan, 2017/03/22 12:29:49]

This is the main change.

+        tr.e.chrome.getInteractiveTimestamps(model);
     for (let rendererHelper of rendererHelpers) {
       if (rendererHelper.isChromeTracingUI) continue;
-      let tasks = rendererHelper.mainThread.sliceGroup.topLevelSlices
+      const tasks = rendererHelper.mainThread.sliceGroup.topLevelSlices
           .filter(slice => slice.duration > 0 && !containsForcedGC_(slice))
           .map(slice => {return {start: slice.start, end: slice.end};});
       totalHistogram.addSample(
@@ -114,15 +116,15 @@ tr.exportTo('tr.metrics.sh', function() {
               rendererHelper.mainThread.bounds.min,
               rendererHelper.mainThread.bounds.max,
               WINDOW_SIZE_MS, tasks));
-      let interactiveTimestamps =
-          tr.e.chrome.getInteractiveTimestamps(model).get(rendererHelper.pid);
+      const interactiveTimestamps =
+        rendererToInteractiveTimestamps.get(rendererHelper.pid);
       if (interactiveTimestamps.length === 0) continue;
       if (interactiveTimestamps.length > 1) {
         // TODO(ulan): Support multiple interactive time windows when
         // https://crbug.com/692112 is fixed.
         continue;
       }
-      let interactiveWindow =
+      const interactiveWindow =
           tr.b.Range.fromExplicitRange(interactiveTimestamps[0], Infinity)
           .findIntersection(rendererHelper.mainThread.bounds);
       interactiveHistogram.addSample(
@@ -131,7 +133,8 @@ tr.exportTo('tr.metrics.sh', function() {
               WINDOW_SIZE_MS, tasks));
     }
     addV8ContributionToExpectedQueueingTime(
-        totalHistogram, interactiveHistogram, histograms, model);
+        totalHistogram, interactiveHistogram, rendererToInteractiveTimestamps,
+        histograms, model);
     histograms.addHistogram(totalHistogram);
     histograms.addHistogram(interactiveHistogram);
   }
@@ -144,15 +147,21 @@ tr.exportTo('tr.metrics.sh', function() {
    * - total:500ms_window:renderer_eqt:v8:gc,
    * - interactive:500ms_window:renderer_eqt:v8:gc:scavenger,
    * - interactive:500ms_window:renderer_eqt:v8:compile.
+   * @param totalEqtHistogram the main total EQT histogram.
+   * @param interactiveEqtHistogram the main interactive EQT histogram.
+   * @param rendererToInteractiveTimestamps a map from renderer pid to an array
+   *     of interactive timestamps.
    */
   function addV8ContributionToExpectedQueueingTime(
-      totalEqtHistogram, interactiveEqtHistogram, histograms, model) {
+      totalEqtHistogram, interactiveEqtHistogram,
+      rendererToInteractiveTimestamps, histograms, model) {
     if (!model.categories.includes('v8')) return;
     const breakdownForTotal = new tr.v.d.RelatedHistogramMap();
     const breakdownForInteractive = new tr.v.d.RelatedHistogramMap();
     for (let [eventName, filter] of V8_EVENT_NAMES_TO_FILTERS) {
       const contribution = contributionToExpectedQueueingTime(
-          filter, eventName, histograms, model);
+          filter, eventName, rendererToInteractiveTimestamps,
+          histograms, model);
       breakdownForTotal.set(eventName, contribution.total);
       breakdownForInteractive.set(eventName, contribution.interactive);
     }
@@ -191,28 +200,31 @@ tr.exportTo('tr.metrics.sh', function() {
    * @param eventPredicate the predicate for selecting events.
    * @param eventName the name describing the selected events. This name will be
    *     added to metric names.
+   * @param rendererToInteractiveTimestamps a map from renderer pid to an array
+   *     of interactive timestamps.
    * @returns {{total: !tr.v.Histogram, interactive: !tr.v.Histogram}}
    */
   function contributionToExpectedQueueingTime(
-      eventPredicate, eventName, histograms, model) {
-    let chromeHelper = model.getOrCreateHelper(
+      eventPredicate, eventName, rendererToInteractiveTimestamps, histograms,
+      model) {
+    const chromeHelper = model.getOrCreateHelper(
         tr.model.helpers.ChromeModelHelper);
-    let totalHistogram = createHistogramForEQT_(
+    const totalHistogram = createHistogramForEQT_(
         `total:${WINDOW_SIZE_MS}ms_window:renderer_eqt:${eventName}`,
         `Contribution to the expected queueing time by ${eventName}` +
         ' for a given renderer. It is computed as the maximum EQT in' +
         ` a ${WINDOW_SIZE_MS}ms sliding window after shrinking top-level` +
         ` tasks to contain only ${eventName} subevents`);
-    let interactiveHistogram = createHistogramForEQT_(
+    const interactiveHistogram = createHistogramForEQT_(
         `interactive:${WINDOW_SIZE_MS}ms_window:renderer_eqt:${eventName}`,
         `Contribution to the expected queueing time by ${eventName}` +
         ' for a given renderer while the page is interactive. It is computed' +
         ` as the maximum EQT in a ${WINDOW_SIZE_MS}ms sliding window after` +
         ` shrinking top-level tasks to contain only ${eventName} subevents`);
-    let rendererHelpers = tr.b.dictionaryValues(chromeHelper.rendererHelpers);
+    const rendererHelpers = tr.b.dictionaryValues(chromeHelper.rendererHelpers);
     for (let rendererHelper of rendererHelpers) {
       if (rendererHelper.isChromeTracingUI) continue;
-      let tasks = rendererHelper.mainThread.sliceGroup.topLevelSlices
+      const tasks = rendererHelper.mainThread.sliceGroup.topLevelSlices
           .filter(slice => slice.duration > 0 && !containsForcedGC_(slice))
           .map(slice => {
             return {
@@ -226,15 +238,15 @@ tr.exportTo('tr.metrics.sh', function() {
               rendererHelper.mainThread.bounds.min,
               rendererHelper.mainThread.bounds.max,
               WINDOW_SIZE_MS, tasks));
-      let interactiveTimestamps =
-          tr.e.chrome.getInteractiveTimestamps(model).get(rendererHelper.pid);
+      const interactiveTimestamps =
+          rendererToInteractiveTimestamps.get(rendererHelper.pid);
       if (interactiveTimestamps.length === 0) continue;
       if (interactiveTimestamps.length > 1) {
         // TODO(ulan): Support multiple interactive time windows when
         // https://crbug.com/692112 is fixed.
         continue;
       }
-      let interactiveWindow =
+      const interactiveWindow =
           tr.b.Range.fromExplicitRange(interactiveTimestamps[0], Infinity)
           .findIntersection(rendererHelper.mainThread.bounds);
       interactiveHistogram.addSample(