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) {
+namespace {
+
+// Returns whether the page moved to the foreground prior to |event|. True if
+// the page was always in the foreground.
+bool MovedToForegroundBefore(const base::TimeDelta& event,
+                             const PageLoadExtraInfo& info) {
+  return info.started_in_foreground || (!info.first_foreground_time.is_zero() &&
+                                        event > info.first_foreground_time);
+}
+
+// Returns whether the page moved to the background after |event|. True if the
+// page never moved to the background.

[Yaron, 2016/02/11 22:07:09]

a little confusing because of this, but would rather not make this even more
verbose :)

+bool MovedToBackgroundAfter(const base::TimeDelta& event,
+                            const PageLoadExtraInfo& info) {
+  return info.first_background_time.is_zero() ||
+         event < info.first_background_time;
+}
+
+}  // namespace
+
+bool StartInForegroundEventInForeground(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);
+         MovedToBackgroundAfter(event, info);
+}
+
+bool StartInBackgroundEventInForeground(const base::TimeDelta& event,
+                                       const PageLoadExtraInfo& info) {

[Yaron, 2016/02/11 22:07:09]

nit: indent

+  return !info.started_in_foreground && !event.is_zero() &&
+         MovedToForegroundBefore(event, info) &&
+         MovedToBackgroundAfter(event, info);
 }
 
 }  // namespace page_load_metrics