Putting histogram names of tracked prefs in tracked_preference_histogram_name file.

components/user_prefs/tracked/tracked_preference_histogram_names.h

Index: components/user_prefs/tracked/tracked_preference_histogram_names.h
diff --git a/components/user_prefs/tracked/tracked_preference_histogram_names.h b/components/user_prefs/tracked/tracked_preference_histogram_names.h
new file mode 100644
index 0000000000000000000000000000000000000000..c5a82a557b5d7c31e9c118b46796f363c0703430
--- /dev/null
+++ b/components/user_prefs/tracked/tracked_preference_histogram_names.h
@@ -0,0 +1,25 @@
+// 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.
+
+#ifndef COMPONENTS_USER_PREFS_TRACKED_TRACKED_PREFERENCE_HISTOGRAM_NAMES_H_
+#define COMPONENTS_USER_PREFS_TRACKED_TRACKED_PREFERENCE_HISTOGRAM_NAMES_H_
+
+namespace user_prefs {
+namespace tracked {
+
+extern const char kTrackedPrefHistogramUnchanged[];
+extern const char kTrackedPrefHistogramCleared[];
+extern const char kTrackedPrefHistogramMigratedLegacyDeviceId[];
+extern const char kTrackedPrefHistogramChanged[];
+extern const char kTrackedPrefHistogramInitialized[];
+extern const char kTrackedPrefHistogramTrustedInitialized[];
+extern const char kTrackedPrefHistogramNullInitialized[];
+extern const char kTrackedPrefHistogramWantedReset[];
+extern const char kTrackedPrefHistogramReset[];
+extern const char kTrackedSplitPrefHistogramChanged[];
+
+}  // namespace tracked
+}  // namespace user_prefs
+
+#endif  // COMPONENTS_USER_PREFS_TRACKED_TRACKED_PREFERENCE_HISTOGRAM_NAMES_H_