Remove call to WasHidden as part of the app being backgrounded.

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 571ef104db8367353264a36aaef54403df502d26..b51abec412d1e3190abe9db62921cd452ee041d5 100644
--- a/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
+++ b/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
@@ -308,10 +308,11 @@ void MetricsWebContentsObserver::OnInputEvent(
 }
 
 void MetricsWebContentsObserver::FlushMetricsOnAppEnterBackground() {
-  // Signal to observers that we've been backgrounded, in cases where the
-  // FlushMetricsOnAppEnterBackground callback gets invoked before the
-  // associated WasHidden callback.
-  WasHidden();
+  // Note that, while a call to FlushMetricsOnAppEnterBackground usually
+  // indicates that the app is about to be backgrounded, there are cases where
+  // the app may not end up getting backgrounded. Thus, we should not assume
+  // anything about foreground / background state of the associated tab as part
+  // of this method call.
 
   if (committed_load_)
     committed_load_->FlushMetricsOnAppEnterBackground();