[Prerender] first contentful paint histograms.

chrome/browser/prerender/prerender_histograms.h

 // Copyright (c) 2012 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_PRERENDER_PRERENDER_HISTOGRAMS_H_
 #define CHROME_BROWSER_PRERENDER_PRERENDER_HISTOGRAMS_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 34 matching lines @@
   PrerenderHistograms();
 
   // Records the perceived page load time for a page - effectively the time from
   // when the user navigates to a page to when it finishes loading.  The actual
   // load may have started prior to navigation due to prerender hints.
   void RecordPerceivedPageLoadTime(Origin origin,
                                    base::TimeDelta perceived_page_load_time,
                                    NavigationType navigation_type,
                                    const GURL& url);
 
+  // Record perceived first contentful paint time for prerendered pages,
+  // analogous to the page load time above.

[pasko, 2016/11/17 19:52:16]

let's copy the relevant parts of the comment from the above because the above
function is likely to go away soon, and when it happens this comment won't be
updated.

[mattcary, 2016/11/18 09:21:11]

Done.

+  void RecordPerceivedFirstContentfulPaintTime(
+      Origin origin,
+      base::TimeDelta perceived_first_contentful_paint);
+
+  // Record that a first contentful paint occured, and whether we were able to
+  // successfuly record the perceived FCP.
+  void RecordPerceivedFirstContentfulPaintStatus(Origin origin,
+                                                 bool successful);
+
   // Records, in a histogram, the percentage of the page load time that had
   // elapsed by the time it is swapped in.  Values outside of [0, 1.0] are
   // invalid and ignored.
   void RecordPercentLoadDoneAtSwapin(Origin origin, double fraction) const;
 
   // Records the actual pageload time of a prerender that has not been swapped
   // in yet, but finished loading.
   void RecordPageLoadTimeNotSwappedIn(Origin origin,
                                       base::TimeDelta page_load_time,
                                       const GURL& url) const;
@@ skipping 49 matching lines @@
                                       bool is_main_resource,
                                       bool is_redirect,
                                       bool is_no_store) const;
 
   // Called when a NoStatePrefetch resource has been loaded. This is called only
   // once per resource, when all redirects have been resolved.
   void RecordPrefetchRedirectCount(Origin origin,
                                    bool is_main_resource,
                                    int redirect_count) const;
 
-  // Records the time to first contentful paint.
-  // Must not be called for prefetch loads (which are never rendered anyway).
+  // Records the time to first contentful paint in the context of NoState
+  // Prefetch.
+
+  // Must be called for an actual page load, and not be called for prefetch
+  // loads (which are never rendered anyway).
   // |is_no_store| must be true if the main resource has a "no-store" cache
   // control HTTP header.
   // |prefetch_age| must be zero if the page was not prefetched.
-  void RecordFirstContentfulPaint(Origin origin,
-                                  bool is_no_store,
-                                  base::TimeDelta time,
-                                  base::TimeDelta prefetch_age);
+  void RecordNoStateFirstContentfulPaint(Origin origin,
+                                         bool is_no_store,
+                                         base::TimeDelta time,
+                                         base::TimeDelta prefetch_age);
 
   // Returns the name of the histogram used to record the time to first
-  // contentful paint.
+  // contentful paint for NoState Prefetch.
   // Exposed for testing.
-  static std::string GetFirstContentfulPaintHistogramName(
+  static std::string GetNoStateFirstContentfulPaintHistogramName(

[pasko, 2016/11/17 19:52:16]

It would be better to make this method private and expand the full histogram
names in tests. This would also protect from accidentally changing what the
function does with all tests unaffected.

(may be better as a separate change)

[mattcary, 2016/11/18 09:21:11]

What I've done here is consistent with how the other tests work, so this is best
left to another change.

       Origin origin,
       bool is_wash,
       bool is_no_store,
       base::TimeDelta prefetch_age);
 
  private:
+  // Returns the name of the histogram used to record the time to first
+  // contentful paint for Prerender.
+  std::string GetPerceivedFirstContentfulPaintHistogramName(Origin origin,
+                                                            bool is_wash);
+
   base::TimeTicks GetCurrentTimeTicks() const;
 
   // Returns the time elapsed since the last prerender happened.
   base::TimeDelta GetTimeSinceLastPrerender() const;
 
   // Returns whether the PrerenderManager is currently within the prerender
   // window - effectively, up to 30 seconds after a prerender tag has been
   // observed.
   bool WithinWindow() const;
 
@@ skipping 19 matching lines @@
   bool seen_pageload_started_after_prerender_;
 
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(PrerenderHistograms);
 };
 
 }  // namespace prerender
 
 #endif  // CHROME_BROWSER_PRERENDER_PRERENDER_HISTOGRAMS_H_