Page load metrics: improve flaky CSSTiming

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 27 matching lines @@
 
 namespace {
 
 // Waits until a PageLoadMetricsMsg_TimingUpdated message IPC is received
 // matching a PageLoadTiming. See WaitForMatchingIPC for details.
 class TimingUpdatedObserver : public content::BrowserMessageFilter {
  public:
   // A bitvector to express which timing fields to match on.
   enum ExpectedTimingFields {
     FIRST_PAINT = 1 << 0,
-    FIRST_CONTENTFUL_PAINT = 1 << 1
+    FIRST_CONTENTFUL_PAINT = 1 << 1,
+    STYLE_UPDATE_BEFORE_FCP = 1 << 2
   };
 
   explicit TimingUpdatedObserver(content::RenderWidgetHost* render_widget_host)
       : content::BrowserMessageFilter(PageLoadMetricsMsgStart) {
     render_widget_host->GetProcess()->AddFilter(this);
 
     // Roundtrip to the IO thread, to ensure that the filter is properly
     // installed.
     content::BrowserThread::PostTaskAndReply(
         content::BrowserThread::IO, FROM_HERE, base::Bind(&base::DoNothing),
@@ skipping 46 matching lines @@
                 WebLoadingBehaviorDocumentWriteBlockReload) {
       --match_document_write_block_reload_;
     }
 
     if (match_document_write_block_reload_ > 0) {
       return true;
     }
 
     if ((!(matching_fields_ & FIRST_PAINT) || timing.first_paint) &&
         (!(matching_fields_ & FIRST_CONTENTFUL_PAINT) ||
-         timing.first_contentful_paint)) {
+         timing.first_contentful_paint) &&
+        (!(matching_fields_ & STYLE_UPDATE_BEFORE_FCP) ||
+         timing.style_sheet_timing.update_style_duration_before_fcp)) {
       // Ensure that any other handlers of this message, for example the real
       // PageLoadMetric observers, get a chance to handle this message before
       // this waiter unblocks.
       content::BrowserThread::PostTask(
           content::BrowserThread::IO, FROM_HERE,
           base::Bind(&TimingUpdatedObserver::BounceTimingUpdate, this, timing,
                      metadata));
     }
     return true;
   }
@@ skipping 586 matching lines @@
 
   histogram_tester_.ExpectTotalCount(
       "Prerender.none_PrefetchTTFCP.Reference.NoStore.Visible", 1);
   histogram_tester_.ExpectTotalCount(
       "Prerender.none_PrefetchTTFCP.Reference.Cacheable.Visible", 0);
 }
 
 IN_PROC_BROWSER_TEST_F(PageLoadMetricsBrowserTest, CSSTiming) {
   ASSERT_TRUE(embedded_test_server()->Start());
 
+  scoped_refptr<TimingUpdatedObserver> fcp_observer =
+      CreateTimingUpdatedObserver();
+  fcp_observer->AddMatchingFields(
+      TimingUpdatedObserver::STYLE_UPDATE_BEFORE_FCP);
+
   // Careful: Blink code clamps timestamps to 5us, so any CSS parsing we do here
   // must take >> 5us, otherwise we'll log 0 for the value and it will remain
   // unset here.
   ui_test_utils::NavigateToURL(
       browser(),
       embedded_test_server()->GetURL("/page_load_metrics/page_with_css.html"));
   NavigateToUntrackedUrl();
+  fcp_observer->WaitForMatchingIPC();
 
   histogram_tester_.ExpectTotalCount(internal::kHistogramFirstContentfulPaint,
                                      1);
   histogram_tester_.ExpectTotalCount(
       "PageLoad.CSSTiming.Parse.BeforeFirstContentfulPaint", 1);
   histogram_tester_.ExpectTotalCount(
       "PageLoad.CSSTiming.Update.BeforeFirstContentfulPaint", 1);
   histogram_tester_.ExpectTotalCount(
       "PageLoad.CSSTiming.ParseAndUpdate.BeforeFirstContentfulPaint", 1);
 }
 
 IN_PROC_BROWSER_TEST_F(PageLoadMetricsBrowserTest, PayloadSize) {
   ASSERT_TRUE(embedded_test_server()->Start());
 
   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);
 }