Add new background abort type.

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 8e0eeb873481d957375f4cbffd01ad1ead3f90d5..937a8edae11862e41d3523712affa5a2c229ba5c 100644
--- a/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
+++ b/chrome/browser/page_load_metrics/metrics_web_contents_observer.cc
@@ -423,6 +423,13 @@ void PageLoadTracker::WebContentsHidden() {
     DCHECK_EQ(started_in_foreground_, foreground_time_.is_null());
     background_time_ = base::TimeTicks::Now();
     ClampBrowserTimestampIfInterProcessTimeTickSkew(&background_time_);
+    // Though most cases where a tab is backgrounded are user initiated, we
+    // can't be certain that we were backgrounded due to a user action. For
+    // example, on Android, the screen times out after a period of inactivity,
+    // resulting in a non-user-initiated backgrounding.
+    const bool abort_is_user_initiated = false;
+    NotifyAbort(ABORT_BACKGROUND, abort_is_user_initiated, background_time_,
+                true);
   }
 
   for (const auto& observer : observers_)