Record stats about kExtensionKnownDisabled with the PrefMetricsService.

chrome/browser/prefs/pref_metrics_service.cc

 // Copyright 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/prefs/pref_metrics_service.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/json/json_string_value_serializer.h"
 #include "base/metrics/histogram.h"
 #include "base/prefs/pref_registry_simple.h"
 #include "base/prefs/pref_service.h"
 #include "base/strings/string_number_conversions.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/browser_shutdown.h"
 // Accessing the Device ID API here is a layering violation.
 // TODO(bbudge) Move the API so it's usable here.
 // http://crbug.com/276485
 #include "chrome/browser/extensions/api/music_manager_private/device_id.h"
 #include "chrome/browser/extensions/extension_prefs.h"

[bbudge, 2013/10/15 18:56:00]

I don't think we need this any more.

[gab, 2013/10/15 19:09:35]

Done.

 #include "chrome/browser/prefs/pref_service_syncable.h"
 #include "chrome/browser/prefs/scoped_user_pref_update.h"
 #include "chrome/browser/prefs/session_startup_pref.h"
 #include "chrome/browser/prefs/synced_pref_change_registrar.h"
 #include "chrome/browser/profiles/incognito_helpers.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/search_engines/template_url_prepopulate_data.h"
 #include "chrome/browser/ui/tabs/pinned_tab_codec.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/pref_names.h"
 #include "components/browser_context_keyed_service/browser_context_dependency_manager.h"
 #include "crypto/hmac.h"
 #include "grit/browser_resources.h"
 #include "net/base/registry_controlled_domains/registry_controlled_domain.h"
 #include "ui/base/resource/resource_bundle.h"
 
 namespace {
 
 const int kSessionStartupPrefValueMax = SessionStartupPref::kPrefValueMax;
 
+// An unregistered preference to fill in indices in kTrackedPrefs below for
+// preferences that aren't defined on every platform. This is fine as the code
+// below (e.g. CheckTrackedPreferences()) skips unregistered preferences and
+// should thus never report any data about that index on the platforms where
+// that preference is unimplemented.
+const char kUnregisteredPreference = "unregistered.preference";

[bbudge, 2013/10/15 18:56:00]

I wonder if an empty string might be a better value. Or you could replace the
'.' by '_' or just 'unregistered'.

[gab, 2013/10/15 19:09:35]

Used "_" -- it's cuter ;)... but more seriously I think that's never likely to
be a real preference name.

+
 // These preferences must be kept in sync with the TrackedPreference enum in
 // tools/metrics/histograms/histograms.xml. To add a new preference, append it
 // to the array and add a corresponding value to the histogram enum.
 const char* kTrackedPrefs[] = {
   prefs::kShowHomeButton,
   prefs::kHomePageIsNewTabPage,
   prefs::kHomePage,
   prefs::kRestoreOnStartup,
   prefs::kURLsToRestoreOnStartup,
   prefs::kExtensionsPref,
   prefs::kGoogleServicesLastUsername,
   prefs::kSearchProviderOverrides,
   prefs::kDefaultSearchProviderSearchURL,
   prefs::kDefaultSearchProviderKeyword,
   prefs::kDefaultSearchProviderName,
 #if !defined(OS_ANDROID)
   prefs::kPinnedTabs,
+#else
+  kUnregisteredPreference,
 #endif
+  prefs::kExtensionKnownDisabled,
 };
 
 static const size_t kSHA256DigestSize = 32;
 
 }  // namespace
 
 PrefMetricsService::PrefMetricsService(Profile* profile)
     : profile_(profile),
       prefs_(profile_->GetPrefs()),
       local_state_(g_browser_process->local_state()),
@@ skipping 383 matching lines @@
 }
 
 bool PrefMetricsService::Factory::ServiceIsNULLWhileTesting() const {
   return false;
 }
 
 content::BrowserContext* PrefMetricsService::Factory::GetBrowserContextToUse(
     content::BrowserContext* context) const {
   return chrome::GetBrowserContextRedirectedInIncognito(context);
 }