Refactor prepareToMeasureValuesAsync to startMeasureValuesAsyn which run test through callback

third_party/WebKit/PerformanceTests/resources/runner.js

Index: third_party/WebKit/PerformanceTests/resources/runner.js
diff --git a/third_party/WebKit/PerformanceTests/resources/runner.js b/third_party/WebKit/PerformanceTests/resources/runner.js
index 3ce2eef328aa5c3d9f2c18c8ec46fe9551aa34bf..7c273b2537945acad178f1b6783e3751f7108cab 100644
--- a/third_party/WebKit/PerformanceTests/resources/runner.js
+++ b/third_party/WebKit/PerformanceTests/resources/runner.js
@@ -170,6 +170,11 @@ if (window.testRunner) {
         if (test.doNotIgnoreInitialRun)
             completedIterations++;
 
+        if (!scheduler) {
+          runner();
+          return;
+        }
+
         if (runner && test.tracingCategories && window.testRunner &&
             window.testRunner.supportTracing) {
             window.testRunner.traceEventsToMeasure = test.traceEventsToMeasure;
@@ -267,7 +272,7 @@ if (window.testRunner) {
 
     PerfTestRunner.prepareToMeasureValuesAsync = function (test) {
         PerfTestRunner.unit = test.unit;
-        start(test);
+        start(test, undefined, test.run);

[Xianzhu, 2017/05/03 17:14:25]

How about:
   start(test, function(task) { task(); }, function() { test.run(); });
?

I think this has the following benefits:
1. avoids change to start();
2. allows such tests to collect trace measurement.
3. allows test.run to access the test object through 'this';

[nednguyen, 2017/05/03 18:21:52]

I tried this first, but doing so lead to invalid test run. :-(

In particular, PerformanceTests/Parser/html-parser-threaded.html will output:

Ignoring warm-up run (undefined ms)
undefined ms
undefined ms
undefined ms
undefined ms
undefined ms
undefined ms
undefined ms
undefined ms
undefined ms
undefined ms
undefined ms
undefined ms
...

[Xianzhu, 2017/05/03 19:16:00]

I see the problem. scheduleNextRun() doesn't support async measurement.

We should have
  start(test, undefined, function() { test.run() });
here, and add
  if (!scheduler) {
    // This is an async measurement test which has its own scheduler.
    runner();
    return;
  }
in scheduleNextRun().

[nednguyen, 2017/05/03 19:18:50]

Acknowledged.

     }
 
     PerfTestRunner.measureValueAsync = function (measuredValue) {