Add metrics for the number of attached displays.

chrome/browser/metrics/chrome_browser_main_extra_parts_metrics.cc

 // Copyright (c) 2013 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 <string>
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/cpu.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/sparse_histogram.h"
 #include "base/sys_info.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "base/time/time.h"
 #include "chrome/browser/about_flags.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/chrome_browser_main.h"
 #include "chrome/browser/mac/bluetooth_utility.h"
 #include "chrome/browser/pref_service_flags_storage.h"
 #include "chrome/browser/shell_integration.h"
 #include "content/public/browser/browser_thread.h"
 #include "ui/base/touch/touch_device.h"
 #include "ui/base/ui_base_switches.h"
 #include "ui/events/event_switches.h"
+#include "ui/gfx/screen.h"
 
 #if defined(OS_LINUX) && !defined(OS_CHROMEOS)
 #include <gnu/libc-version.h>
 
 #include "base/version.h"
 #if defined(USE_X11)
 #include "ui/base/x/x11_util.h"
 #endif
 #endif  // defined(OS_LINUX) && !defined(OS_CHROMEOS)
 
@@ skipping 175 matching lines @@
     return;
   }
 
   UMA_HISTOGRAM_ENUMERATION("Touchscreen.TouchEventsEnabled", state,
                             UMA_TOUCH_EVENTS_STATE_COUNT);
 }
 
 }  // namespace
 
 ChromeBrowserMainExtraPartsMetrics::ChromeBrowserMainExtraPartsMetrics() {
+  display_count_ = gfx::Screen::GetNativeScreen()->GetNumDisplays();
+  UMA_HISTOGRAM_COUNTS_100("DisplayCount.StartUp", display_count_);

[Ilya Sherman, 2014/10/14 06:34:22]

nit: Please name this "Display.Count.StartUp" (or, even better IMO,
"Display.Count.AtStartUp".  The important part here is to have the group name be
"Display" rather than "DisplayCount", so that there's room to add additional
display metrics if they become useful over time.

[erikchen, 2014/10/14 23:09:38]

Went with "Hardware.Display.Count.OnStartup".

+  gfx::Screen::GetNativeScreen()->AddObserver(this);
 }
 
 ChromeBrowserMainExtraPartsMetrics::~ChromeBrowserMainExtraPartsMetrics() {
+  gfx::Screen::GetNativeScreen()->RemoveObserver(this);
 }
 
 void ChromeBrowserMainExtraPartsMetrics::PreProfileInit() {
   RecordMicroArchitectureStats();
 }
 
 void ChromeBrowserMainExtraPartsMetrics::PreBrowserStart() {
   about_flags::PrefServiceFlagsStorage flags_storage_(
       g_browser_process->local_state());
   about_flags::RecordUMAStatistics(&flags_storage_);
 }
 
 void ChromeBrowserMainExtraPartsMetrics::PostBrowserStart() {
   RecordLinuxGlibcVersion();
 #if defined(USE_X11) && !defined(OS_CHROMEOS)
   UMA_HISTOGRAM_ENUMERATION("Linux.WindowManager",
                             GetLinuxWindowManager(),
                             UMA_LINUX_WINDOW_MANAGER_COUNT);
 #endif
   RecordTouchEventState();
 
   const int kStartupMetricsGatheringDelaySeconds = 45;
   content::BrowserThread::GetBlockingPool()->PostDelayedTask(
       FROM_HERE,
       base::Bind(&RecordStartupMetricsOnBlockingPool),
       base::TimeDelta::FromSeconds(kStartupMetricsGatheringDelaySeconds));
 }
 
+void ChromeBrowserMainExtraPartsMetrics::OnDisplayAdded(
+    const gfx::Display& new_display) {
+  EmitDisplaysChangedMetric();
+}
+
+void ChromeBrowserMainExtraPartsMetrics::OnDisplayRemoved(
+    const gfx::Display& old_display) {
+  EmitDisplaysChangedMetric();
+}
+
+void ChromeBrowserMainExtraPartsMetrics::OnDisplayMetricsChanged(
+    const gfx::Display& display,
+    uint32_t changed_metrics) {
+}
+
+void ChromeBrowserMainExtraPartsMetrics::EmitDisplaysChangedMetric() {
+  int display_count = gfx::Screen::GetNativeScreen()->GetNumDisplays();
+  if (display_count != display_count_) {
+    display_count_ = display_count;
+    UMA_HISTOGRAM_COUNTS_100("DisplayCount.Changed", display_count_);

[Ilya Sherman, 2014/10/14 06:34:22]

nit: And correspondingly, please name this "Display.Count.Changed" (or
"Display.Count.OnChange").

[erikchen, 2014/10/14 23:09:38]

Went with "Hardware.Display.Count.OnChange".

+  }
+}
+
 namespace chrome {
 
 void AddMetricsExtraParts(ChromeBrowserMainParts* main_parts) {
   main_parts->AddParts(new ChromeBrowserMainExtraPartsMetrics());
 }
 
 }  // namespace chrome