Putting histogram names of tracked prefs in tracked_preference_histogram_name file.

components/user_prefs/tracked/pref_names.cc

 // Copyright 2015 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 "components/user_prefs/tracked/pref_names.h"
 
 namespace user_prefs {
 
 // A timestamp (stored in base::Time::ToInternalValue format) of the last time
 // a preference was reset.
 const char kPreferenceResetTime[] = "prefs.preference_reset_time";
 
 }  // namespace user_prefs
+
+namespace user_tracked_prefs {
+
+const char kTrackedPreferenceUnchanged[] =
+    "Settings.TrackedPreferenceUnchanged";
+const char kTrackedPreferenceCleared[] = "Settings.TrackedPreferenceCleared";
+const char kTrackedPreferenceMigratedLegacyDeviceId[] =
+    "Settings.TrackedPreferenceMigratedLegacyDeviceId";
+const char kTrackedPreferenceChanged[] = "Settings.TrackedPreferenceChanged";
+const char kTrackedPreferenceInitialized[] =
+    "Settings.TrackedPreferenceInitialized";
+const char kTrackedPreferenceTrustedInitialized[] =
+    "Settings.TrackedPreferenceTrustedInitialized";
+const char kTrackedPreferenceNullInitialized[] =
+    "Settings.TrackedPreferenceNullInitialized";
+const char kTrackedPreferenceWantedReset[] =
+    "Settings.TrackedPreferenceWantedReset";
+const char kTrackedPreferenceReset[] = "Settings.TrackedPreferenceReset";
+const char kTrackedSplitPreferenceChanged[] =
+    "Settings.TrackedSplitPreferenceChanged.";
+
+}  // namespace user_tracked_prefs.