Buffer cross frame paint timing updates.

chrome/browser/page_load_metrics/metrics_web_contents_observer.cc

Index: chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
diff --git a/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc b/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
index fe9f281890e4a367400eaeb18e15b0cdaee2880e..c3d51772e51a866aa5e1c1ee5db76eab89f79177 100644
--- a/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
+++ b/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
@@ -103,10 +103,20 @@ MetricsWebContentsObserver* MetricsWebContentsObserver::CreateForWebContents(
   return metrics;
 }
 
-MetricsWebContentsObserver::~MetricsWebContentsObserver() {
+MetricsWebContentsObserver::~MetricsWebContentsObserver() {}
+
+void MetricsWebContentsObserver::WebContentsDestroyed() {
   // TODO(csharrison): Use a more user-initiated signal for CLOSE.
   NotifyPageEndAllLoads(END_CLOSE, UserInitiatedInfo::NotUserInitiated());
 
+  // We tear down PageLoadTrackers in WebContentsDestroyed, rather than in the
+  // destructor, since |web_contents()| returns nullptr in the destructor, and
+  // PageLoadMetricsObservers can cause code to execute that wants to be able to
+  // access the current WebContents.
+  committed_load_ = nullptr;
+  provisional_loads_.clear();
+  aborted_provisional_loads_.clear();
+
   for (auto& observer : testing_observers_)
     observer.OnGoingAway();
 }