Loosen FirstMeaningfulPaint UMA network-idle heuristics

chrome/browser/page_load_metrics/page_load_metrics_browsertest.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/files/scoped_temp_dir.h"
 #include "base/macros.h"
 #include "base/test/histogram_tester.h"
 #include "base/time/time.h"
 #include "chrome/browser/page_load_metrics/metrics_web_contents_observer.h"
 #include "chrome/browser/page_load_metrics/observers/aborts_page_load_metrics_observer.h"
@@ skipping 618 matching lines @@
 }
 
 IN_PROC_BROWSER_TEST_F(PageLoadMetricsBrowserTest,
                        FirstMeaningfulPaintRecorded) {
   ASSERT_TRUE(embedded_test_server()->Start());
 
   ui_test_utils::NavigateToURL(browser(),
                                embedded_test_server()->GetURL("/title1.html"));
 
   // Wait until the renderer finishes observing layouts.
-  const int kNetworkIdleTime = 500;
+  const int kNetworkIdleTime = 3000;
   const int kMargin = 500;
   const std::string javascript = base::StringPrintf(
       "setTimeout(() => window.domAutomationController.send(true), %d)",
       kNetworkIdleTime + kMargin);
   bool result;
   EXPECT_TRUE(content::ExecuteScriptAndExtractBool(
       browser()->tab_strip_model()->GetActiveWebContents(),
       javascript, &result));
   EXPECT_TRUE(result);
 
@@ skipping 93 matching lines @@
   ui_test_utils::NavigateToURL(browser(), embedded_test_server()->GetURL(
                                               "/page_load_metrics/large.html"));
   NavigateToUntrackedUrl();
 
   histogram_tester_.ExpectTotalCount(internal::kHistogramTotalBytes, 1);
 
   // Verify that there is a single sample recorded in the 10kB bucket (the size
   // of the main HTML response).
   histogram_tester_.ExpectBucketCount(internal::kHistogramTotalBytes, 10, 1);
 }