Add a histogram for delay between first paint and client side redirects.

components/page_load_metrics/browser/metrics_web_contents_observer.cc

Index: components/page_load_metrics/browser/metrics_web_contents_observer.cc
diff --git a/components/page_load_metrics/browser/metrics_web_contents_observer.cc b/components/page_load_metrics/browser/metrics_web_contents_observer.cc
index a90e574f9c9239db700707c45a16269e40bbca4d..617d7d6d211ed1b8283e168b81edebda28cde8f5 100644
--- a/components/page_load_metrics/browser/metrics_web_contents_observer.cc
+++ b/components/page_load_metrics/browser/metrics_web_contents_observer.cc
@@ -46,6 +46,8 @@ const char kAbortChainSizeSameURL[] =
     "PageLoad.Internal.ProvisionalAbortChainSize.SameURL";
 const char kAbortChainSizeNoCommit[] =
     "PageLoad.Internal.ProvisionalAbortChainSize.NoCommit";
+const char kClientRedirectDelayAfterPaint[] =
+    "PageLoad.Internal.ClientRedirectDelayAfterPaint";
 
 }  // namespace internal
 
@@ -385,6 +387,19 @@ void PageLoadTracker::OnInputEvent(const blink::WebInputEvent& event) {
   }
 }
 
+void PageLoadTracker::NotifyClientRedirectTo(
+    const PageLoadTracker& destination) {
+  base::TimeDelta redirect_delay_after_paint;
+  if (!timing_.first_paint.is_zero()) {
+    base::TimeTicks first_paint_time = navigation_start() + timing_.first_paint;
+    if (destination.navigation_start() > first_paint_time)
+      redirect_delay_after_paint =
+          destination.navigation_start() - first_paint_time;
+  }
+  PAGE_LOAD_HISTOGRAM(internal::kClientRedirectDelayAfterPaint,

[Charlie Harrison, 2016/06/29 20:18:37]

I don't think it's necessary but let's keep in mind cases where
destination.navigation_start() < first_paint_time will get bucketed to zero
here. It may be worthwhile to have a histogram separating those out (as opposed
to combined with cases where the page did not paint at all).

+                      redirect_delay_after_paint);
+}
+
 bool PageLoadTracker::UpdateTiming(const PageLoadTiming& new_timing,
                                    const PageLoadMetadata& new_metadata) {
   // Throw away IPCs that are not relevant to the current navigation.
@@ -720,6 +735,12 @@ void MetricsWebContentsObserver::DidFinishNavigation(
   if (navigation_handle->IsSamePage())
     return;
 
+  if (!navigation_handle->HasUserGesture() &&
+      (navigation_handle->GetPageTransition() &
+       ui::PAGE_TRANSITION_CLIENT_REDIRECT) != 0 &&
+      committed_load_)
+    committed_load_->NotifyClientRedirectTo(*finished_nav);
+
   // Notify other loads that they may have been aborted by this committed load.
   // Note that by using the committed navigation start as the abort cause, we
   // lose data on provisional loads that were aborted by other provisional