mac: Add metrics for AppKit Fullscreen style.

chrome/browser/metrics/chrome_browser_main_extra_parts_metrics_mac.mm

+// Copyright 2014 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/chrome_browser_main_extra_parts_metrics.h"
+
+#include "base/mac/sdk_forward_declarations.h"
+#include "base/metrics/histogram.h"
+
+namespace {
+
+// The possible values of the setting "Screens Have Separate Spaces".
+enum SeparateSpaces {
+  SCREENS_HAVE_SEPARATE_SPACES = 0,
+  SCREENS_HAVE_SHARED_SPACES = 1,
+  SEPARATE_SPACES_COUNT = 2
+};
+
+}  // namespace
+
+void ChromeBrowserMainExtraPartsMetrics::RecordMacMetrics() {
+  BOOL screens_have_separate_spaces =
+      [NSScreen respondsToSelector:@selector(screensHaveSeparateSpaces)] &&

[Robert Sesek, 2014/10/20 17:34:46]

You may want to collect !respondsToSelector:#selector(screensHaveSeparateFaces)
under a separate enum value.

[erikchen, 2014/10/20 18:30:59]

I expect your suggested metric to be almost identical to users on 10.9+ vs users
on 10.8 and older. Do you have reason to believe otherwise?

[Robert Sesek, 2014/10/20 18:54:36]

Right, my suggestion would separate out users that do not have this option.

[erikchen, 2014/10/21 18:44:38]

Done.

+      [NSScreen screensHaveSeparateSpaces];
+  int separate_spaces = screens_have_separate_spaces
+                            ? SCREENS_HAVE_SEPARATE_SPACES
+                            : SCREENS_HAVE_SHARED_SPACES;
+  UMA_HISTOGRAM_ENUMERATION("OSX.Settings.ScreensHaveSeparateSpaces",
+                            separate_spaces,
+                            SEPARATE_SPACES_COUNT);
+}