[perf] Fix test timeout for jetstream2 on android pixel2 bots

Bug: 1002936
Change-Id: I88eb87fa44f15461007ceb05a6cbc9171e9b1b1e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1817147
Commit-Queue: Haiyang Pan <hypan@google.com>
Reviewed-by: Michael Hablich <hablich@chromium.org>
Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#701369}

tools/perf/expectations.config

@@ -128,9 +128,6 @@ crbug.com/894147 [ android-nexus-5x ] blink_perf.svg/SierpinskiCarpet.html [ Ski
 # Benchmark: jetstream
 crbug.com/830600 [ android-nexus-5x android-webview ] jetstream/http://browserbench.org/JetStream/ [ Skip ]
 
-# Benchmark: jetstream2
-crbug.com/1002936 [ android-pixel-2 ] jetstream2/http://browserbench.org/JetStream/ [ Skip ]
-
 # Benchmark: loading.desktop
 crbug.com/723783 [ win ] loading.desktop/Orange_cold [ Skip ]
 crbug.com/723783 [ win ] loading.desktop/Orange_warm [ Skip ]

tools/perf/page_sets/jetstream2_pages.py

@@ -14,6 +14,11 @@ class Jetstream2Story(press_story.PressStory):
 
   def ExecuteTest(self, action_runner):
     action_runner.tab.WaitForDocumentReadyStateToBeComplete()
+    # Wait till the elements with selector "#results>.benchmark" are available
+    # as they are required for running "JetStream.start()"
+    action_runner.WaitForJavaScriptCondition("""
+        document.querySelectorAll("#results>.benchmark").length > 0
+        """, timeout=5)
     action_runner.EvaluateJavaScript('JetStream.start()')
 
   def ParseTestResults(self, action_runner):