Add Startup.BrowserView.FirstPaint / .CompositingEnded histograms.

chrome/browser/metrics/browser_view_histogram_helper.h

+// 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.
+
+#ifndef CHROME_BROWSER_METRICS_BROWSER_VIEW_HISTOGRAM_HELPER_H_
+#define CHROME_BROWSER_METRICS_BROWSER_VIEW_HISTOGRAM_HELPER_H_
+
+#include "base/macros.h"
+#include "base/scoped_observer.h"
+#include "base/time/time.h"
+#include "ui/compositor/compositor_observer.h"
+
+// Class that encapsulates logic of recording
+// Startup.BrowserView.Paint-histograms.
+class BrowserViewHistogramHelper : public ui::CompositorObserver {

[sky, 2017/04/12 19:34:08]

BrowserView is specific to views, please name this BrowserWindowHistogramHelper.

[themblsha, 2017/04/17 17:34:49]

Done.

+ public:
+  BrowserViewHistogramHelper();
+  ~BrowserViewHistogramHelper() override;
+
+  // Call this when the Browser finishes painting its UI, and the user will see
+  // it after next Compositor frame swap.
+  // |compositor| is the compositor that composites the just-painted Browser
+  // widget, or nullptr in Cocoa (we're using CoreAnimation's compositor there).
+  void OnBrowserPainted(ui::Compositor* compositor);
+
+ private:
+  void RemoveCompositorObserver();
+
+  // ui::CompositorObserver:
+  void OnCompositingDidCommit(ui::Compositor* compositor) override {}
+  void OnCompositingStarted(ui::Compositor* compositor,
+                            base::TimeTicks start_time) override;
+  void OnCompositingLockStateChanged(ui::Compositor* compositor) override {}
+  void OnCompositingShuttingDown(ui::Compositor* compositor) override;
+
+  ScopedObserver<ui::Compositor, ui::CompositorObserver> scoped_observer_;
+  bool did_first_paint_ = false;
+
+  DISALLOW_COPY_AND_ASSIGN(BrowserViewHistogramHelper);
+};
+
+#endif  // CHROME_BROWSER_METRICS_BROWSER_VIEW_HISTOGRAM_HELPER_H_