Don't include abort() cost when timing MSE methods.

tools/perf/page_sets/mse_cases/startup_test.js

Index: tools/perf/page_sets/mse_cases/startup_test.js
diff --git a/tools/perf/page_sets/mse_cases/startup_test.js b/tools/perf/page_sets/mse_cases/startup_test.js
index 98f714b90164546244d949291c260f7e25cbbb7a..282bde7ce5fca1c43506e5faca991c9963491ce7 100644
--- a/tools/perf/page_sets/mse_cases/startup_test.js
+++ b/tools/perf/page_sets/mse_cases/startup_test.js
@@ -375,12 +375,11 @@
         return;
       }
 
+      var testEndTime = getPerfTimestamp();
       for (var i = 0; i < appenders.length; ++i) {
         appenders[i].onPlaybackStarted(mediaSource);
       }
 
-      var testEndTime = getPerfTimestamp();
-
       testDone = true;
       window.clearInterval(listener);
       window.clearTimeout(timeout);