Optional <TimeDelta> since they may be non existent.

components/page_load_metrics/browser/metrics_web_contents_observer.h

Index: components/page_load_metrics/browser/metrics_web_contents_observer.h
diff --git a/components/page_load_metrics/browser/metrics_web_contents_observer.h b/components/page_load_metrics/browser/metrics_web_contents_observer.h
index d58cfb003b594b0b803b1b3b7fa8befb7d2354ab..db872caf2425022fc46faba7f50a2a4edf8699b9 100644
--- a/components/page_load_metrics/browser/metrics_web_contents_observer.h
+++ b/components/page_load_metrics/browser/metrics_web_contents_observer.h
@@ -87,6 +87,12 @@ enum InternalErrorLoadEvent {
   // latest aborted load is used to track the chain size.
   ERR_NAVIGATION_SIGNALS_MULIPLE_ABORTED_LOADS,
 
+  // A TimeTicks value in the browser process has value less than
+  // navigation_start_. This could happen if the navigation_start_ was computed
+  // in the renderer process and the system clock has inter process time tick
+  // skew.
+  ERR_INTER_PROCESS_TIME_TICK_SKEW,

[Charlie Harrison, 2016/05/24 19:32:01]

Looks like you need to update histograms.xml with this new enum value.

[shivanisha, 2016/05/24 20:09:56]

Done. Thanks.

+
   // Add values before this final count.
   ERR_LAST_ENTRY
 };
@@ -143,8 +149,15 @@ class PageLoadTracker {
   // If the user performs some abort-like action while we are tracking this page
   // load, notify the tracker. Note that we may not classify this as an abort if
   // we've already performed a first paint.
-  void NotifyAbort(UserAbortType abort_type, base::TimeTicks timestamp);
-  void UpdateAbort(UserAbortType abort_type, base::TimeTicks timestamp);
+  // is_browser_timestamp signifies if the timestamp passed is taken in the
+  // browser process or not. We need this to possibly clamp browser timestamp on
+  // a machine with inter process time tick skew.
+  void NotifyAbort(UserAbortType abort_type,
+                   base::TimeTicks timestamp,
+                   bool is_browser_timestamp);
+  void UpdateAbort(UserAbortType abort_type,
+                   base::TimeTicks timestamp,
+                   bool is_browser_timestamp);
 
   // This method returns true if this page load has been aborted with type of
   // ABORT_OTHER, and the |abort_cause_time| is within a sufficiently close
@@ -161,11 +174,20 @@ class PageLoadTracker {
     return url_;
   }
 
+  PageLoadExtraInfo ComputePageLoadExtraInfo();
+
  private:
-  PageLoadExtraInfo GetPageLoadMetricsInfo();
+  // This function converts a TimeTicks value taken in the browser process
+  // to navigation_start_ if:
+  // - base::TimeTicks is not comparable across processes because the clock
+  // is not system wide monotonic.
+  // - *event_time < navigation_start_
+  void ClampBrowserTimestampIfInterProcessTimeTickSkew(
+      base::TimeTicks* event_time);
 
   void UpdateAbortInternal(UserAbortType abort_type,
-                           base::TimeTicks timestamp);
+                           base::TimeTicks timestamp,
+                           bool is_browser_timestamp);
 
   // If |final_navigation| is null, then this is an "unparented" abort chain,
   // and represents a sequence of provisional aborts that never ends with a
@@ -251,6 +273,9 @@ class MetricsWebContentsObserver
   void WasHidden() override;
   void RenderProcessGone(base::TerminationStatus status) override;
 
+  // This getter function is required for testing.
+  const PageLoadExtraInfo GetPageLoadExtraInfoForCommittedLoad();
+
  private:
   friend class content::WebContentsUserData<MetricsWebContentsObserver>;
 
@@ -258,7 +283,8 @@ class MetricsWebContentsObserver
   // that might abort them.
   void NotifyAbortAllLoads(UserAbortType abort_type);
   void NotifyAbortAllLoadsWithTimestamp(UserAbortType abort_type,
-                                        base::TimeTicks timestamp);
+                                        base::TimeTicks timestamp,
+                                        bool is_browser_timestamp);
   // Notify aborted provisional loads that a new navigation occurred. This is
   // used for more consistent attribution tracking for aborted provisional
   // loads. This method returns the provisional load that was likely aborted by