predictors: Mark before_first_contentful_paint for resources fetched before fcp.

chrome/browser/page_load_metrics/observers/resource_prefetch_predictor_page_load_metrics_observer.cc

 // Copyright 2017 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/observers/resource_prefetch_predictor_page_load_metrics_observer.h"
 
 #include "base/memory/ptr_util.h"
 #include "chrome/browser/page_load_metrics/page_load_metrics_util.h"
 #include "chrome/browser/predictors/resource_prefetch_predictor.h"
 #include "chrome/browser/predictors/resource_prefetch_predictor_factory.h"
@@ skipping 12 matching lines @@
 
 // static
 std::unique_ptr<ResourcePrefetchPredictorPageLoadMetricsObserver>
 ResourcePrefetchPredictorPageLoadMetricsObserver::CreateIfNeeded(
     content::WebContents* web_contents) {
   predictors::ResourcePrefetchPredictor* predictor =
       predictors::ResourcePrefetchPredictorFactory::GetForProfile(
           web_contents->GetBrowserContext());
   if (!predictor)
     return nullptr;
+  predictors::NavigationID navigation_id(web_contents);

[alexilin, 2017/03/17 14:46:46]

I'm afraid it won't work correctly.
The observer is created before navigation commit, at this point we don't know
navigation final destination. NavigationID contains main_frame_url it has to be
created after navigation commit.

You could keep a pointer to web_contents inside the class and create
NavigationID directly in OnFirstContentfulPaint().

[trevordixon, 2017/03/27 12:30:08]

Done.

   return base::MakeUnique<ResourcePrefetchPredictorPageLoadMetricsObserver>(
-      predictor);
+      predictor, navigation_id);
 }
 
 ResourcePrefetchPredictorPageLoadMetricsObserver::
     ResourcePrefetchPredictorPageLoadMetricsObserver(
-        predictors::ResourcePrefetchPredictor* predictor)
-    : predictor_(predictor) {
+        predictors::ResourcePrefetchPredictor* predictor,
+        predictors::NavigationID navigation_id)
+    : predictor_(predictor), navigation_id_(navigation_id) {
   DCHECK(predictor_);
 }
 
 ResourcePrefetchPredictorPageLoadMetricsObserver::
     ~ResourcePrefetchPredictorPageLoadMetricsObserver() {}
 
 page_load_metrics::PageLoadMetricsObserver::ObservePolicy
 ResourcePrefetchPredictorPageLoadMetricsObserver::OnStart(
     content::NavigationHandle* navigation_handle,
     const GURL& currently_commited_url,
     bool started_in_foreground) {
   return (started_in_foreground &&
           predictor_->IsUrlPrefetchable(navigation_handle->GetURL()))
              ? CONTINUE_OBSERVING
              : STOP_OBSERVING;
 }
 
 page_load_metrics::PageLoadMetricsObserver::ObservePolicy
 ResourcePrefetchPredictorPageLoadMetricsObserver::OnHidden(
     const page_load_metrics::PageLoadTiming& timing,
     const page_load_metrics::PageLoadExtraInfo& extra_info) {
   return STOP_OBSERVING;
 }
 
 void ResourcePrefetchPredictorPageLoadMetricsObserver::OnFirstContentfulPaint(
     const page_load_metrics::PageLoadTiming& timing,
     const page_load_metrics::PageLoadExtraInfo& extra_info) {
+  predictor_->RecordFirstContentfulPaint(navigation_id_);
   PAGE_LOAD_HISTOGRAM(
       internal::kHistogramResourcePrefetchPredictorFirstContentfulPaint,
       timing.first_contentful_paint.value());
 }
 
 void ResourcePrefetchPredictorPageLoadMetricsObserver::OnFirstMeaningfulPaint(
     const page_load_metrics::PageLoadTiming& timing,
     const page_load_metrics::PageLoadExtraInfo& extra_info) {
   PAGE_LOAD_HISTOGRAM(
       internal::kHistogramResourcePrefetchPredictorFirstMeaningfulPaint,
       timing.first_meaningful_paint.value());
 }