Fix a race condition in preference metric reporting.

chrome/browser/prefs/chrome_pref_service_factory.cc

 // Copyright (c) 2012 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/chrome_pref_service_factory.h"
 
 #include "base/bind.h"
 #include "base/debug/trace_event.h"
 #include "base/file_util.h"
 #include "base/files/file_path.h"
 #include "base/metrics/histogram.h"
 #include "base/prefs/default_pref_store.h"
 #include "base/prefs/json_pref_store.h"
 #include "base/prefs/pref_notifier_impl.h"
 #include "base/prefs/pref_registry.h"
 #include "base/prefs/pref_service.h"
 #include "base/prefs/pref_value_store.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/prefs/command_line_pref_store.h"
+#include "chrome/browser/prefs/pref_change_reporter.h"
+#include "chrome/browser/prefs/pref_hash_store.h"
 #include "chrome/browser/prefs/pref_model_associator.h"
 #include "chrome/browser/prefs/pref_service_syncable_builder.h"
 #include "chrome/browser/ui/profile_error_dialog.h"
 #include "components/user_prefs/pref_registry_syncable.h"
 #include "content/public/browser/browser_context.h"
 #include "content/public/browser/browser_thread.h"
 #include "grit/chromium_strings.h"
 #include "grit/generated_resources.h"
 
 #if defined(ENABLE_CONFIGURATION_POLICY)
@@ skipping 40 matching lines @@
 #endif
   }
 }
 
 void PrepareBuilder(
     PrefServiceSyncableBuilder* builder,
     const base::FilePath& pref_filename,
     base::SequencedTaskRunner* pref_io_task_runner,
     policy::PolicyService* policy_service,
     ManagedUserSettingsService* managed_user_settings,
+    scoped_ptr<PrefHashStore> pref_hash_store,
     const scoped_refptr<PrefStore>& extension_prefs,
     bool async) {
 #if defined(OS_LINUX)
   // We'd like to see what fraction of our users have the preferences
   // stored on a network file system, as we've had no end of troubles
   // with NFS/AFS.
   // TODO(evanm): remove this once we've collected state.
   file_util::FileSystemType fstype;
   if (file_util::GetFileSystemType(pref_filename.DirName(), &fstype)) {
     UMA_HISTOGRAM_ENUMERATION("PrefService.FileSystemType",
@@ skipping 19 matching lines @@
     builder->WithSupervisedUserPrefs(
         new SupervisedUserPrefStore(managed_user_settings));
   }
 #endif
 
   builder->WithAsync(async);
   builder->WithExtensionPrefs(extension_prefs.get());
   builder->WithCommandLinePrefs(
       new CommandLinePrefStore(CommandLine::ForCurrentProcess()));
   builder->WithReadErrorCallback(base::Bind(&HandleReadError));
-  builder->WithUserPrefs(new JsonPrefStore(pref_filename, pref_io_task_runner));
+
+  scoped_refptr<JsonPrefStore> pref_store(
+      new JsonPrefStore(pref_filename, pref_io_task_runner));
+
+  ReportPrefStoreChangesToUMA(pref_store.get(), pref_hash_store.Pass());

[gab, 2013/11/27 23:43:27]

Consider a more generic name; this could later be augmented to do more than
simple reporting.

+
+  builder->WithUserPrefs(pref_store.get());

[gab, 2013/11/27 23:43:27]

FYI, looks like this changed in https://codereview.chromium.org/64193003

 }
 
 }  // namespace
 
 namespace chrome_prefs {
 
 PrefService* CreateLocalState(
     const base::FilePath& pref_filename,
     base::SequencedTaskRunner* pref_io_task_runner,
     policy::PolicyService* policy_service,
     const scoped_refptr<PrefRegistry>& pref_registry,
     bool async) {
   PrefServiceSyncableBuilder builder;
   PrepareBuilder(&builder,
                  pref_filename,
                  pref_io_task_runner,
                  policy_service,
                  NULL,
+                 scoped_ptr<PrefHashStore>(),
                  NULL,
                  async);
   return builder.Create(pref_registry.get());
 }
 
 PrefServiceSyncable* CreateProfilePrefs(
     const base::FilePath& pref_filename,
     base::SequencedTaskRunner* pref_io_task_runner,
     policy::PolicyService* policy_service,
     ManagedUserSettingsService* managed_user_settings,
+    scoped_ptr<PrefHashStore> pref_hash_store,
     const scoped_refptr<PrefStore>& extension_prefs,
     const scoped_refptr<user_prefs::PrefRegistrySyncable>& pref_registry,
     bool async) {
   TRACE_EVENT0("browser", "chrome_prefs::CreateProfilePrefs");
   PrefServiceSyncableBuilder builder;
   PrepareBuilder(&builder,
                  pref_filename,
                  pref_io_task_runner,
                  policy_service,
                  managed_user_settings,
+                 pref_hash_store.Pass(),
                  extension_prefs,
                  async);
   return builder.CreateSyncable(pref_registry.get());
 }
 
 }  // namespace chrome_prefs