FirstMeaningfulPaint UMA

chrome/browser/page_load_metrics/metrics_web_contents_observer.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 "chrome/browser/page_load_metrics/metrics_web_contents_observer.h"
 
 #include <algorithm>
 #include <ostream>
 #include <string>
 #include <utility>
@@ skipping 208 matching lines @@
     observer->OnDomContentLoadedEventStart(new_timing, extra_info);
   if (new_timing.load_event_start && !last_timing.load_event_start)
     observer->OnLoadEventStart(new_timing, extra_info);
   if (new_timing.first_layout && !last_timing.first_layout)
     observer->OnFirstLayout(new_timing, extra_info);
   if (new_timing.first_paint && !last_timing.first_paint)
     observer->OnFirstPaint(new_timing, extra_info);
   if (new_timing.first_text_paint && !last_timing.first_text_paint)
     observer->OnFirstTextPaint(new_timing, extra_info);
   if (new_timing.first_image_paint && !last_timing.first_image_paint)
     observer->OnFirstImagePaint(new_timing, extra_info);

[Bryan McQuade, 2016/07/29 15:02:26]

there's also some logic in this file that validates that the various events in a
PageLoadTiming are in order (see the calls to EventsInOrder). Can you add a
call, something like:

if (!EventsInOrder(timing.first_paint, timing.first_meaningful_paint)) {
  NOTREACHED() << ...;
  return false;
}

and there's some similar code in the test harness that makes sure timing data is
populated correctly which you'll need to update as well.

[Kunihiko Sakamoto, 2016/08/01 08:52:06]

Done.
The only ordering we can guarantee is FP <= FMP.

[Kunihiko Sakamoto, 2016/08/02 03:19:37]

Um, actually that wasn't true...
If the page has no foreground elements, FMP may be first (empty) paint where FP
is not recorded.

In patch set 4 I've made FMPDetector skip background-only paints.

   if (new_timing.first_contentful_paint && !last_timing.first_contentful_paint)
     observer->OnFirstContentfulPaint(new_timing, extra_info);
+  if (new_timing.first_meaningful_paint && !last_timing.first_meaningful_paint)
+    observer->OnFirstMeaningfulPaint(new_timing, extra_info);
   if (new_timing.parse_start && !last_timing.parse_start)
     observer->OnParseStart(new_timing, extra_info);
   if (new_timing.parse_stop && !last_timing.parse_stop)
     observer->OnParseStop(new_timing, extra_info);
   if (extra_info.metadata.behavior_flags != last_metadata.behavior_flags)
     observer->OnLoadingBehaviorObserved(extra_info);
 }
 
 }  // namespace
 
@@ skipping 709 matching lines @@
     if (navigation_handle->IsSamePage() || navigation_handle->IsErrorPage())
       return false;
     const std::string& mime_type = web_contents()->GetContentsMimeType();
     if (mime_type != "text/html" && mime_type != "application/xhtml+xml")
       return false;
   }
   return true;
 }
 
 }  // namespace page_load_metrics