Add Startup.BrowserView.FirstPaint / .CompositingEnded histograms.

chrome/browser/ui/browser_view_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/ui/browser_view_histogram_helper.h"
+
+#include "components/startup_metric_utils/browser/startup_metric_utils.h"
+#include "ui/compositor/compositor.h"
+
+BrowserViewHistogramHelper::BrowserViewHistogramHelper()
+    : scoped_observer_(this) {}
+
+BrowserViewHistogramHelper::~BrowserViewHistogramHelper() {
+  RemoveCompositorObserver();

[sky, 2017/04/11 17:13:36]

Doesn't ~ScopedObserver take care of this for you?

[themblsha, 2017/04/12 17:18:28]

Correct. Removed the call but the destructor still lives on because of 'Complex
class/struct needs an explicit out-of-line destructor.'

+}
+
+void BrowserViewHistogramHelper::OnDidPaintChildren(
+    ui::Compositor* compositor) {
+  if (!did_first_paint_) {

[sky, 2017/04/11 17:13:36]

Early out rather than big conditional.

[themblsha, 2017/04/12 17:18:28]

Done.

+    did_first_paint_ = true;
+
+    startup_metric_utils::RecordBrowserViewFirstPaint(base::TimeTicks::Now());
+
+#if defined(OS_MACOSX)
+    if (!compositor) {
+      // In Cocoa version of Chromium UI is rendered inside the main process
+      // using CoreAnimation compositor, and at this point everything is already
+      // visible to the user.
+      startup_metric_utils::RecordBrowserViewFirstPaintCompositingEnded(
+          base::TimeTicks::Now());
+      return;
+    }
+#endif  // OS_MACOSX
+
+    scoped_observer_.Add(compositor);
+  }
+}
+
+void BrowserViewHistogramHelper::RemoveCompositorObserver() {
+  scoped_observer_.RemoveAll();
+}
+
+// OnCompositingEnded was removed crbug.com/671202, this is the next best thing.
+void BrowserViewHistogramHelper::OnCompositingStarted(
+    ui::Compositor* compositor,
+    base::TimeTicks start_time) {
+  startup_metric_utils::RecordBrowserViewFirstPaintCompositingEnded(
+      base::TimeTicks::Now());
+
+  RemoveCompositorObserver();
+}
+
+void BrowserViewHistogramHelper::OnCompositingShuttingDown(
+    ui::Compositor* compositor) {
+  RemoveCompositorObserver();
+}