[throughput] Add a new test case for extreme janky main thread

This CL adds a new throughput test story, to test the cases where the
main thread is extremely jank, and that the throughput can be 0.

Bug: 1048187
Change-Id: Ifdd44d165652489de8b41965921801894fba86f5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2134929Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#756493}

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

@@ -34,10 +34,12 @@ const skipEvery = targetMainFps > 0 ? parseInt(60 / targetMainFps) : 0;
 
 const query = window.location.search.substr(1).split('&');
 const shouldJank = query.indexOf('jank') >= 0;
+const shouldExtremeJank = query.indexOf('extremejank') >= 0;
 const offscreen = query.indexOf('offscreen') >= 0;
 if (offscreen) {
   document.body.style.marginTop = '5000px';
 }
+const jankAmount = shouldExtremeJank ? 5000 : 16;
 
 var currentValue = 0;
 const maxValue = 150;
@@ -61,9 +63,9 @@ function animateStep() {
       if (currentValue <= minValue)
         incrementing = true;
     }
-    if (shouldJank) {
+    if (shouldJank || shouldExtremeJank) {
       const now = new Date();
-      while ((new Date() - now) < 16) {}
+      while ((new Date() - now) < jankAmount) {}
     }
     mainanim.style[attributeName] = setProp(currentValue);
   }

tools/perf/page_sets/rendering/throughput_test_cases.py

@@ -112,6 +112,13 @@ class MainSixtyWithJankImplZero(ThroughputMetricStory):
          'main-animations-throughput.html?jank#60')
 
 
+class MainSixtyWithExtremeJankImplZero(ThroughputMetricStory):
+  BASE_NAME = 'main_60fps_with_extreme_jank_impl_0fps'
+  SUPPORTED_PLATFORMS = platforms.ALL_PLATFORMS
+  URL = ('file://../../../../chrome/test/data/perf/throughput_test_cases/'
+         'main-animations-throughput.html?extremejank#60')
+
+
 class MainZeroWithJankImplZero(ThroughputMetricStory):
   BASE_NAME = 'main_0fps_with_jank_impl_0fps'
   SUPPORTED_PLATFORMS = platforms.ALL_PLATFORMS