Fix a throughput test case

This particular test case was changed here:
https://chromium-review.googlesource.com/c/chromium/src/+/2022618

And that CL made a mistake. In particular, it added a shouldDelay
which is meant to be used to delay the start of the main-thread
animation, but shouldDelay is not used.

This CL fixes that.

Bug: None
Change-Id: Ia8c2c1fea0918aee69ff07808969d7ac70f48cd9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2154819
Commit-Queue: Xida Chen <xidachen@chromium.org>
Reviewed-by: Yi Gu <yigu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#760210}

chrome/test/data/perf/throughput_test_cases/main-impl-animations-throughput.html

@@ -55,7 +55,7 @@ const skipEvery = targetMainFps > 0 ? parseInt(60 / targetMainFps) : 0;
 
 const query = window.location.search.substr(1).split('&');
 const shouldJank = query.indexOf('jank') >= 0;
-// Delay the start of the main thread animation by 2 seconds to test the
+// Delay the start of the main thread animation by 1 seconds to test the
 // aggregation of the main and compositor thread throughput.
 const shouldDelay = query.indexOf('delay') >= 0;
 
@@ -72,8 +72,9 @@ var frameCount = 0;
 var startTime;
 
 function animateStep() {
-  if (skipEvery && ++frameCount % skipEvery == 0 &&
-      (new Date() - startTime) >= 1000) {
+  const shouldStart = (skipEvery && ++frameCount % skipEvery == 0) &&
+    (!shouldDelay || (new Date() - startTime) >= 1000);
+  if (shouldStart) {
     if (incrementing) {
       currentValue += valueChange;
       if (currentValue >= maxValue)