Add Startup.BrowserView.FirstPaint / .CompositingEnded histograms.

chrome/browser/metrics/browser_window_histogram_helper.cc

+// Copyright 2017 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/metrics/browser_window_histogram_helper.h"
+
+#include "components/startup_metric_utils/browser/startup_metric_utils.h"
+#include "ui/compositor/compositor.h"
+
+BrowserWindowHistogramHelper::BrowserWindowHistogramHelper(
+    ui::Compositor* compositor)
+    : scoped_observer_(this) {
+  startup_metric_utils::RecordBrowserWindowFirstPaint(base::TimeTicks::Now());
+
+#if defined(OS_MACOSX)
+  if (!compositor) {
+    // In Cocoa version of Chromium UI is rendered inside the main process using

[Alexei Svitkine (slow), 2017/04/18 16:01:31]

Nit: Add a , after Chromium

[themblsha, 2017/04/19 15:06:09]

Done.

+    // CoreAnimation compositor, and at this point everything is already visible
+    // to the user.
+    startup_metric_utils::RecordBrowserWindowFirstPaintCompositingEnded(
+        base::TimeTicks::Now());
+    return;
+  }
+#endif  // OS_MACOSX
+
+  scoped_observer_.Add(compositor);
+}
+
+BrowserWindowHistogramHelper::~BrowserWindowHistogramHelper() {}
+
+// static
+std::unique_ptr<BrowserWindowHistogramHelper>
+BrowserWindowHistogramHelper::OnBrowserPainted(ui::Compositor* compositor) {

[Alexei Svitkine (slow), 2017/04/18 16:01:31]

Can this be named in some way that makes it clear that it returns the helper?

e.g.

MaybeCreateInstanceOnPaint()

[themblsha, 2017/04/19 15:06:09]

Done.

+  static bool did_first_paint = false;
+  if (did_first_paint)
+    return std::unique_ptr<BrowserWindowHistogramHelper>();
+
+  did_first_paint = true;
+
+  return std::unique_ptr<BrowserWindowHistogramHelper>(

[Alexei Svitkine (slow), 2017/04/18 16:01:32]

Nit: MakeUnique

[themblsha, 2017/04/19 15:06:09]

I was unable to make it work with private constructor. Am I missing something
here?

+      new BrowserWindowHistogramHelper(compositor));
+}
+
+// OnCompositingEnded was removed crbug.com/671202, this is the next best thing.
+void BrowserWindowHistogramHelper::OnCompositingStarted(
+    ui::Compositor* compositor,
+    base::TimeTicks start_time) {
+  startup_metric_utils::RecordBrowserWindowFirstPaintCompositingEnded(
+      base::TimeTicks::Now());
+
+  scoped_observer_.RemoveAll();
+}
+
+void BrowserWindowHistogramHelper::OnCompositingShuttingDown(
+    ui::Compositor* compositor) {
+  scoped_observer_.RemoveAll();
+}