Add Startup.BrowserView.FirstPaint / .CompositingEnded histograms.

chrome/browser/metrics/startup_metrics_browsertest.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 <set>
+
+#include "base/metrics/histogram_samples.h"
+#include "base/metrics/statistics_recorder.h"
+#include "base/run_loop.h"
+#include "chrome/test/base/in_process_browser_test.h"
+
+using StartupMetricsTest = InProcessBrowserTest;
+
+namespace {
+
+constexpr const char* kStartupMetrics[] = {
+    "Startup.BrowserView.FirstPaint",
+    "Startup.BrowserView.FirstPaint.CompositingEnded",
+};
+
+}  // namespace
+
+// RecordBrowserViewFirstPaint and RecordBrowserViewFirstPaintCompositingEnded
+// have a static variables inside, so we can't run several tests inside a single
+// process, and thus this test cannot be in unit_tests.
+
+// Tests that the specified startup-specific histograms are indeed reported.
+IN_PROC_BROWSER_TEST_F(StartupMetricsTest, ReportsValues) {
+  for (auto* const histogram : kStartupMetrics) {
+    while (!base::StatisticsRecorder::FindHistogram(histogram)) {

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

no {}

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

Done.

+      base::RunLoop().RunUntilIdle();
+    }
+  }
+}