Optional <TimeDelta> since they may be non existent.

components/page_load_metrics/browser/metrics_web_contents_observer.h

 // 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.
 
 #ifndef COMPONENTS_PAGE_LOAD_METRICS_BROWSER_METRICS_WEB_CONTENTS_OBSERVER_H_
 #define COMPONENTS_PAGE_LOAD_METRICS_BROWSER_METRICS_WEB_CONTENTS_OBSERVER_H_
 
 #include <map>
 #include <memory>
 #include <vector>
@@ skipping 69 matching lines @@
   // cc file for details). We use this error counter to understand how often it
   // happens.
   ERR_ABORT_BEFORE_NAVIGATION_START,
 
   // A new navigation triggers abort updates in multiple trackers in
   // |aborted_provisional_loads_|, when usually there should only be one (the
   // navigation that just aborted because of this one). If this happens, the
   // 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
 };
 
 // This class serves as a functional interface to various chrome// features.
 // Impl version is defined in chrome/browser/page_load_metrics.
 class PageLoadMetricsEmbedderInterface {
  public:
   virtual ~PageLoadMetricsEmbedderInterface() {}
   virtual bool IsPrerendering(content::WebContents* web_contents) = 0;
@@ skipping 36 matching lines @@
   }
 
   UserAbortType abort_type() const { return abort_type_; }
   base::TimeTicks abort_time() const { return abort_time_; }
 
   void AddObserver(std::unique_ptr<PageLoadMetricsObserver> observer);
 
   // 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
   // delta to when it was aborted. Note that only provisional loads can be
   // aborted with ABORT_OTHER. While this heuristic is coarse, it works better
   // and is simpler than other feasible methods. See https://goo.gl/WKRG98.
   bool IsLikelyProvisionalAbort(base::TimeTicks abort_cause_time);
 
   bool MatchesOriginalNavigation(content::NavigationHandle* navigation_handle);
 
   // Only valid to call post-commit.
   const GURL& committed_url() const {
     DCHECK(!commit_time_.is_null());
     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
   // committed load.
   void LogAbortChainHistograms(content::NavigationHandle* final_navigation);
 
   // Whether the renderer should be sending timing IPCs to this page load.
   bool renderer_tracked_;
 
   // The navigation start in TimeTicks, not the wall time reported by Blink.
@@ skipping 65 matching lines @@
       content::NavigationHandle* navigation_handle) override;
   void DidFinishNavigation(
       content::NavigationHandle* navigation_handle) override;
   void DidRedirectNavigation(
       content::NavigationHandle* navigation_handle) override;
   void NavigationStopped() override;
   void WasShown() override;
   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>;
 
   // Notify all loads, provisional and committed, that we performed an action
   // 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
   // this navigation, to help instantiate the new PageLoadTracker.
   std::unique_ptr<PageLoadTracker> NotifyAbortedProvisionalLoadsNewNavigation(
       content::NavigationHandle* new_navigation);
 
   void OnTimingUpdated(content::RenderFrameHost*,
                        const PageLoadTiming& timing,
                        const PageLoadMetadata& metadata);
@@ skipping 23 matching lines @@
 
   // Has the MWCO observed at least one navigation?
   bool has_navigated_;
 
   DISALLOW_COPY_AND_ASSIGN(MetricsWebContentsObserver);
 };
 
 }  // namespace page_load_metrics
 
 #endif  // COMPONENTS_PAGE_LOAD_METRICS_BROWSER_METRICS_WEB_CONTENTS_OBSERVER_H_