Record first paint in UKM.

chrome/browser/page_load_metrics/observers/ukm_page_load_metrics_observer.h

 // 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.
 
 #ifndef CHROME_BROWSER_PAGE_LOAD_METRICS_OBSERVERS_UKM_PAGE_LOAD_METRICS_OBSERVER_H_
 #define CHROME_BROWSER_PAGE_LOAD_METRICS_OBSERVERS_UKM_PAGE_LOAD_METRICS_OBSERVER_H_
 
 #include "base/macros.h"
 #include "base/optional.h"
 #include "base/time/time.h"
 #include "chrome/browser/page_load_metrics/page_load_metrics_observer.h"
 #include "components/ukm/ukm_service.h"
 #include "net/nqe/network_quality_estimator.h"
 #include "ui/base/page_transition_types.h"
 
 namespace content {
 class WebContents;
 }
 
 namespace internal {
 
 // Name constants are exposed here so they can be referenced from tests.
 extern const char kUkmPageLoadEventName[];
 extern const char kUkmParseStartName[];
 extern const char kUkmDomContentLoadedName[];
 extern const char kUkmLoadEventName[];
+extern const char kUkmFirstPaintName[];
 extern const char kUkmFirstContentfulPaintName[];
 extern const char kUkmFirstMeaningfulPaintName[];
 extern const char kUkmForegroundDurationName[];
 extern const char kUkmFailedProvisionaLoadName[];
 extern const char kUkmNetErrorCode[];
 extern const char kUkmEffectiveConnectionType[];
 extern const char kUkmHttpRttEstimate[];
 extern const char kUkmTransportRttEstimate[];
 extern const char kUkmPageTransition[];
 
@@ skipping 60 matching lines @@
   base::Optional<base::TimeDelta> http_rtt_estimate_;
   base::Optional<base::TimeDelta> transport_rtt_estimate_;
 
   // PAGE_TRANSITION_LINK is the default PageTransition value.
   ui::PageTransition page_transition_ = ui::PAGE_TRANSITION_LINK;
 
   DISALLOW_COPY_AND_ASSIGN(UkmPageLoadMetricsObserver);
 };
 
 #endif  // CHROME_BROWSER_PAGE_LOAD_METRICS_OBSERVERS_UKM_PAGE_LOAD_METRICS_OBSERVER_H_