Histogram the amount of time spent on HTTP(S) page loads

chrome/browser/page_load_metrics/observers/https_page_load_metrics_observer.cc

+// Copyright 2016 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 "chrome/browser/page_load_metrics/observers/https_page_load_metrics_observer.h"
+
+#include "base/metrics/histogram_macros.h"
+#include "url/url_constants.h"
+
+HttpsPageLoadMetricsObserver::HttpsPageLoadMetricsObserver()
+    : time_travelled_backwards_(false) {}
+
+void HttpsPageLoadMetricsObserver::OnCommit(
+    content::NavigationHandle* navigation_handle,
+    bool started_in_foreground) {
+  url_ = navigation_handle->GetURL();
+  if (started_in_foreground)
+    OnShown();
+}
+
+void HttpsPageLoadMetricsObserver::OnHidden() {
+  base::Time current_time = base::Time::Now();
+  currently_in_foreground_ = false;
+
+  // Backwards time travel can occur if (a) the device has gone through a time
+  // machine, or (b) the client's clock was changed. Record backwards time
+  // travel to invalidate the statistics for this page.
+  if (last_time_shown_ > current_time) {

[Charlie Harrison, 2016/04/25 13:20:08]

If you used TimeTicks you wouldn't have to worry about this problem (except in
extremely rare cases of computers with broken clocks).

The only annoying thing about TimeTicks is that they don't tick when the
computer is in suspend mode. I suspect that actually helps you in this case,
though.

[felt, 2016/04/25 21:30:04]

Ahh, good point. Done.
Yes, that's actually a great property.

+    time_travelled_backwards_ = true;
+    return;
+  }
+
+  foreground_time_ += current_time - last_time_shown_;
+}
+
+void HttpsPageLoadMetricsObserver::OnShown() {
+  last_time_shown_ = base::Time::Now();
+  currently_in_foreground_ = true;
+}
+
+void HttpsPageLoadMetricsObserver::OnComplete(
+    const page_load_metrics::PageLoadTiming& timing,
+    const page_load_metrics::PageLoadExtraInfo& extra_info) {
+  if (time_travelled_backwards_ || !url_.is_valid())

[Charlie Harrison, 2016/04/25 13:20:08]

You'll also might want to filter out results if the page never committed (i.e. a
connection wasn't successfully made to the server).

Additionally, PageLoadTiming& contains useful metrics about page load time that
you might want to filter by. For instance, you may want to only track pages that
painted contents on the screen.

[felt, 2016/04/25 21:30:04]

Good point. I've switched to using the committed URL from extra_info.
OK, added some more checks. I'm assuming that the paint will never actually
happen in 0 time.

+    return;
+
+  if (currently_in_foreground_)
+    OnHidden();
+
+  if (url_.SchemeIs(url::kHttpsScheme))
+    UMA_HISTOGRAM_LONG_TIMES_100("Navigation.Time.HTTPS", foreground_time_);
+  else if (url_.SchemeIs(url::kHttpScheme))
+    UMA_HISTOGRAM_LONG_TIMES_100("Navigation.Time.HTTP", foreground_time_);
+  else
+    UMA_HISTOGRAM_LONG_TIMES_100("Navigation.Time.Other", foreground_time_);
+}