[CustomTabs] Report the navigation start as absolute time

chrome/android/java/src/org/chromium/chrome/browser/metrics/PageLoadMetrics.java

 // Copyright 2016 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.
 
 package org.chromium.chrome.browser.metrics;
 
 import org.chromium.base.ObserverList;
 import org.chromium.base.ThreadUtils;
 import org.chromium.base.annotations.CalledByNative;
 import org.chromium.content_public.browser.WebContents;
 
 /**
  * Receives the page load metrics updates from AndroidPageLoadMetricsObserver, and notifies the
  * observers.
  *
  * Threading: everything here must happen on the UI thread.
  */
 public class PageLoadMetrics {
     public static final String FIRST_CONTENTFUL_PAINT = "firstContentfulPaint";
+    public static final String NAVIGATION_START = "navigationStart";
 
     /** Observer for page load metrics. */
     public interface Observer {
         /**
          * Called when the first contentful paint page load metric is available.
          *
          * @param webContents the WebContents this metrics is related to.
+         * @param navigationStartTick Absolute navigation start time, as TimeTicks.
          * @param firstContentfulPaintMs Time to first contentful paint from navigation start.
          */
-        public void onFirstContentfulPaint(WebContents webContents, long firstContentfulPaintMs);
+        public void onFirstContentfulPaint(
+                WebContents webContents, long navigationStartMs, long firstContentfulPaintMs);
     }
 
     private static ObserverList<Observer> sObservers;
 
     /** Adds an observer. */
     public static boolean addObserver(Observer observer) {
         ThreadUtils.assertOnUiThread();
         if (sObservers == null) sObservers = new ObserverList<>();
         return sObservers.addObserver(observer);
     }
 
     /** Removes an observer. */
     public static boolean removeObserver(Observer observer) {
         ThreadUtils.assertOnUiThread();
         if (sObservers == null) return false;
         return sObservers.removeObserver(observer);
     }
 
     @CalledByNative
-    static void onFirstContentfulPaint(WebContents webContents, long firstContentfulPaintMs) {
+    static void onFirstContentfulPaint(
+            WebContents webContents, long navigationStartTick, long firstContentfulPaintMs) {
         ThreadUtils.assertOnUiThread();
         if (sObservers == null) return;
         for (Observer observer : sObservers) {
-            observer.onFirstContentfulPaint(webContents, firstContentfulPaintMs);
+            observer.onFirstContentfulPaint(
+                    webContents, navigationStartTick, firstContentfulPaintMs);
         }
     }
 
     private PageLoadMetrics() {}
 }