Refactor prepareToMeasureValuesAsync to startMeasureValuesAsyn which run test through callback

third_party/WebKit/PerformanceTests/BlinkGC/resources/measure-gc.js

 if (!window.PerfTestRunner)
     console.log("measure-gc.js requires PerformanceTests/resources/runner.js to be loaded.");
 if (!window.internals)
     console.log("measure-gc.js requires window.internals.");
 if (!window.GCController && !window.gc)
     console.log("measure-gc.js requires GCController or exposed gc().");
 
 (function (PerfTestRunner) {
     var warmUpCount = 3;
     var completedIterations = 0;
 
     PerfTestRunner.measureBlinkGCTime = function(test) {
         if (!test.unit)
             test.unit = 'ms';
         if (!test.warmUpCount)
             test.warmUpCount = warmUpCount;
+        if (!test.run)
+            test.run = function() {};
 
         completedIterations = 0;
         PerfTestRunner.prepareToMeasureValuesAsync(test);
 
         // Force a V8 GC before running Blink GC test to avoid measuring marking from stale V8 wrappers.
         if (window.GCController)
             GCController.collectAll();
         else if (window.gc) {
             for (var i = 0; i < 7; i++)
                 gc();
@@ skipping 16 matching lines @@
             var end = PerfTestRunner.now();
             PerfTestRunner.measureValueAsync((end - start) / NumberOfGCRunsPerForceBlinkGC);
             setTimeout(runTest, 0);
 
             if (completedIterations > warmUpCount)
                 console.timeEnd("BlinkGCTimeMeasurement");
             completedIterations++;
         }, 0);
     }
 })(window.PerfTestRunner);