[Prerender] first contentful paint histograms.

chrome/browser/prerender/prerender_tab_helper.cc

Index: chrome/browser/prerender/prerender_tab_helper.cc
diff --git a/chrome/browser/prerender/prerender_tab_helper.cc b/chrome/browser/prerender/prerender_tab_helper.cc
index 096705dc8ab5c57a1f271d56271684e192e30a71..1aae2ea609343c5e18f3a7a7c6bb8c5bf4d76c70 100644
--- a/chrome/browser/prerender/prerender_tab_helper.cc
+++ b/chrome/browser/prerender/prerender_tab_helper.cc
@@ -26,16 +26,7 @@ PrerenderTabHelper::PrerenderTabHelper(content::WebContents* web_contents)
       origin_(ORIGIN_NONE),
       next_load_is_control_prerender_(false),
       next_load_origin_(ORIGIN_NONE),
-      weak_factory_(this) {
-  // Determine if this is a prerender.
-  PrerenderManager* prerender_manager = MaybeGetPrerenderManager();
-  if (prerender_manager &&
-      prerender_manager->IsWebContentsPrerendering(web_contents, &origin_)) {
-    navigation_type_ = NAVIGATION_TYPE_PRERENDERED;
-  } else {
-    navigation_type_ = NAVIGATION_TYPE_NORMAL;
-  }
-}
+      weak_factory_(this) {}
 
 PrerenderTabHelper::~PrerenderTabHelper() {
 }
@@ -106,12 +97,22 @@ void PrerenderTabHelper::DidStartProvisionalLoadForFrame(
     const GURL& validated_url,
     bool is_error_page,
     bool is_iframe_srcdoc) {
+  // Determine the navigation type.
+  PrerenderManager* prerender_manager = MaybeGetPrerenderManager();
+  if (prerender_manager &&
+      prerender_manager->IsWebContentsPrerendering(web_contents(), &origin_)) {
+    navigation_type_ = NAVIGATION_TYPE_PRERENDERED;
+  } else {
+    navigation_type_ = NAVIGATION_TYPE_NORMAL;
+  }
+
   if (render_frame_host->GetParent())
     return;
 
   // Record PPLT state for the beginning of a new navigation.
   pplt_load_start_ = GetTimeTicksFromPrerenderManager();
   actual_load_start_ = base::TimeTicks();
+  last_load_ = GetTimeTicksFromPrerenderManager();

[Bryan McQuade, 2016/11/18 15:46:42]

the reference start time that all page load metrics time deltas are measured
from is NavigationHandle::NavigationStart() - can we use that instead?

Perhaps you can override OnStart and record the navigation start time in your
observer, and then instead of passing the timedelta for FCP to prerendermanager,
you can instead pass navigation_start + first_contentful_paint TimeTicks, so you
have the absolute time that the FCP happened, which you can then subtract
last_swap_ from to get the perceived delta.

[mattcary, 2016/11/21 11:05:00]

Done, although there seems no nice way to test due to the need to mock out the
NavigationHandle. I instead allow one to set the start time on the observer
directly, which means ::OnStart is not directly tested. The logic there is very
simple, though, so I think that's the best we can do. Contradiction welcome :)

 
   if (next_load_is_control_prerender_) {
     DCHECK_EQ(NAVIGATION_TYPE_NORMAL, navigation_type_);
@@ -156,10 +157,10 @@ void PrerenderTabHelper::PrerenderSwappedIn() {
   // Ensure we are not prerendering any more.
   DCHECK_EQ(NAVIGATION_TYPE_PRERENDERED, navigation_type_);
   DCHECK(!IsPrerendering());
+  last_swap_ = GetTimeTicksFromPrerenderManager();
   if (pplt_load_start_.is_null()) {
     // If we have already finished loading, report a 0 PPLT.
     RecordPerceivedPageLoadTime(base::TimeDelta(), 1.0);
-    DCHECK_EQ(NAVIGATION_TYPE_NORMAL, navigation_type_);
   } else {
     // If we have not finished loading yet, record the actual load start, and
     // rebase the start time to now.
@@ -173,6 +174,17 @@ void PrerenderTabHelper::WouldHavePrerenderedNextLoad(Origin origin) {
   next_load_origin_ = origin;
 }
 
+bool PrerenderTabHelper::LoadToPerceivedDelta(base::TimeDelta* delta) {
+  if (!last_load_.is_null() && !last_swap_.is_null() &&
+      last_swap_ >= last_load_) {
+    if (delta) {
+      *delta = last_swap_ - last_load_;
+    }
+    return true;
+  }
+  return false;
+}
+
 void PrerenderTabHelper::RecordPerceivedPageLoadTime(
     base::TimeDelta perceived_page_load_time,
     double fraction_plt_elapsed_at_swap_in) {
@@ -188,10 +200,6 @@ void PrerenderTabHelper::RecordPerceivedPageLoadTime(
   prerender_manager->RecordPerceivedPageLoadTime(
       origin_, navigation_type_, perceived_page_load_time,
       fraction_plt_elapsed_at_swap_in, url_);
-
-  // Reset state for the next navigation.
-  navigation_type_ = NAVIGATION_TYPE_NORMAL;
-  origin_ = ORIGIN_NONE;
 }
 
 }  // namespace prerender