Refactor prepareToMeasureValuesAsync to startMeasureValuesAsyn which run test through callback

third_party/WebKit/PerformanceTests/Bindings/post-message.html

Index: third_party/WebKit/PerformanceTests/Bindings/post-message.html
diff --git a/third_party/WebKit/PerformanceTests/Bindings/post-message.html b/third_party/WebKit/PerformanceTests/Bindings/post-message.html
index 5745861725132670f3077a95aa054a06e76a1375..52d1bdc7898ae7b5f219d45b8aee641033f8b13d 100644
--- a/third_party/WebKit/PerformanceTests/Bindings/post-message.html
+++ b/third_party/WebKit/PerformanceTests/Bindings/post-message.html
@@ -27,12 +27,12 @@ function testDone() {
 }
 
 window.onload = function () {
-    PerfTestRunner.prepareToMeasureValuesAsync({
+    PerfTestRunner.startMeasureValuesAsync({
         description: "Measures time to run 1000 postMessage round trips in serial.",
         unit: 'ms',
+        run: runTest,
         done: testDone,
     });
-    runTest();
 };
 </script>
 <div id="log"></div>