Add metric with time between background tab being foregrounded and the first paint

components/page_load_metrics/browser/page_load_metrics_util.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/page_load_metrics/browser/page_load_metrics_util.h"
 
 #include <algorithm>
 
 #include "components/page_load_metrics/browser/page_load_metrics_observer.h"
 #include "components/page_load_metrics/common/page_load_timing.h"
 
 namespace page_load_metrics {
 
-bool EventOccurredInForeground(const base::TimeDelta& event,
-                               const PageLoadExtraInfo& info) {
-  return info.started_in_foreground && !event.is_zero() &&
-         (info.first_background_time.is_zero() ||
-          event < info.first_background_time);
+namespace {
+
+// Returns true if:
+// - We have timing information for the event.
+// - The event occurred prior to the page being moved to the background.
+bool InForeground(base::TimeDelta event, const PageLoadExtraInfo& info) {

[Charlie Harrison, 2016/02/22 23:25:56]

nit: Why not "EventInForeground" for symmetry? I like this though.

+  if (event.is_zero())
+    return false;
+
+  if (!info.started_in_foreground &&
+      (info.first_foreground_time.is_zero() ||
+       event < info.first_foreground_time)) {
+    return false;
+  }
+
+  return info.first_background_time.is_zero() ||
+         event < info.first_background_time;
+}
+
+}  // namespace
+
+bool StartInForegroundEventInForeground(base::TimeDelta event,
+                                        const PageLoadExtraInfo& info) {
+  return info.started_in_foreground && InForeground(event, info);
+}
+
+bool StartInBackgroundEventInForeground(base::TimeDelta event,
+                                        const PageLoadExtraInfo& info) {
+  return !info.started_in_foreground && InForeground(event, info);
 }
 
 }  // namespace page_load_metrics