[Metrics] Move CachingPermutedEntropyProvider into the variations component.

components/variations/pref_names.h

Index: components/variations/pref_names.h
diff --git a/components/variations/pref_names.h b/components/variations/pref_names.h
new file mode 100644
index 0000000000000000000000000000000000000000..19fd9c235ba7455a4682e898a63341e856c43e96
--- /dev/null
+++ b/components/variations/pref_names.h
@@ -0,0 +1,18 @@
+// Copyright 2014 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_VARIATIONS_PREF_NAMES_H_
+#define COMPONENTS_VARIATIONS_PREF_NAMES_H_
+
+namespace metrics {
+namespace prefs {
+
+// Alphabetical list of preference names specific to the variations component.
+// Keep alphabetized, and document each in the .cc file.
+extern const char kVariationsPermutedEntropyCache[];
+
+}  // namespace prefs
+}  // namespace metrics
+
+#endif  // COMPONENTS_VARIATIONS_PREF_NAMES_H_