Add Startup.BrowserView.FirstPaint / .CompositingEnded histograms.

chrome/browser/ui/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_UI_BROWSER_VIEW_HISTOGRAM_HELPER_H_
+#define CHROME_BROWSER_UI_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, 2017/04/11 17:13:36]

This class is only used for metrics recording. I think it makes more sense to
live in c/b/metrics?

[themblsha, 2017/04/12 17:18:29]

Done. But I'm not sure how to add it to the GN in that case: please look at the
updated chrome/browser/ui/BUILD.gn (this file still makes sense only in ui)

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

The new file should be in the target that contains the other files in
c/b/metrics. That is, chrome/browser:browser.

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

Thanks! Moved, also updated histogram names.

+ public:
+  BrowserViewHistogramHelper();
+  ~BrowserViewHistogramHelper();

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

override

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

Ah yes, I currently don't have the https://codereview.chromium.org/2791613002
that breaks compilation that I submitted last week :-) Done.

+
+  void OnDidPaintChildren(ui::Compositor* compositor);

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

Document this. Also, that it happens to be called from PaintChildren is an
implementation detail of views. How about naming this OnBrowserPainted()?

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

Better name, thanks! Renamed.

+
+ 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_UI_BROWSER_VIEW_HISTOGRAM_HELPER_H_