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 ScreenSpacesConfiguration {
+  SCREENS_CANNOT_HAVE_SEPARATE_SPACES = 0,
+  SCREENS_HAVE_SEPARATE_SPACES = 1,
+  SCREENS_HAVE_SHARED_SPACES = 2,
+  SCREEN_SPACES_CONFIGURATION_COUNT = 3
+};
+
+}  // namespace
+
+void ChromeBrowserMainExtraPartsMetrics::RecordMacMetrics() {
+  ScreenSpacesConfiguration separate_spaces =
+      SCREENS_CANNOT_HAVE_SEPARATE_SPACES;
+
+  if ([NSScreen respondsToSelector:@selector(screensHaveSeparateSpaces)]) {
+    BOOL screens_have_separate_spaces = [NSScreen screensHaveSeparateSpaces];
+    separate_spaces = screens_have_separate_spaces
+                          ? SCREENS_HAVE_SEPARATE_SPACES
+                          : SCREENS_HAVE_SHARED_SPACES;
+  }
+  UMA_HISTOGRAM_ENUMERATION("OSX.Settings.ScreensHaveSeparateSpaces",
+                            separate_spaces,
+                            SCREEN_SPACES_CONFIGURATION_COUNT);
+}