updated the gmail story script

Checking this pinpoint task: https://pinpoint-dot-chromeperf.appspot.com/job/1484ef632c0000
Before this change only one frame_time was recorded and the value is not normal (~3ms)
And by updating the story more than 700 frame_times are recorded and the value is (~26ms)

Bug: chromium:965578
Change-Id: I2646755c138f33618da32f6ac5a02e8534dd7459
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1622505
Commit-Queue: Behdad Bakhshinategh <behdadb@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#662726}

tools/perf/page_sets/rendering/top_real_world_desktop.py

@@ -335,7 +335,8 @@ class Gmail2018SmoothPage(TopRealWorldDesktopPage):
     super(Gmail2018SmoothPage, self).RunNavigateSteps(action_runner)
     action_runner.WaitForJavaScriptCondition(
         'window.gmonkey !== undefined &&'
-        'document.getElementById("gb") !== null')
+        'document.getElementById("gb") !== null &&'
+        'document.readyState == "complete"')
 
   def RunPageInteractions(self, action_runner):
     action_runner.WaitForElement(selector='.Tm.aeJ')