Introduce a new framework for back-and-forth tracked/protected preferences migration.

chrome/browser/prefs/tracked/tracked_preferences_migration.h

Index: chrome/browser/prefs/tracked/tracked_preferences_migration.h
diff --git a/chrome/browser/prefs/tracked/tracked_preferences_migration.h b/chrome/browser/prefs/tracked/tracked_preferences_migration.h
new file mode 100644
index 0000000000000000000000000000000000000000..6411cddf19757aba441e4c1978354c35209d8aa6
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+++ b/chrome/browser/prefs/tracked/tracked_preferences_migration.h
@@ -0,0 +1,36 @@
+// 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 CHROME_BROWSER_PREFS_TRACKED_TRACKED_PREFERENCES_MIGRATION_H_
+#define CHROME_BROWSER_PREFS_TRACKED_TRACKED_PREFERENCES_MIGRATION_H_
+
+#include <set>
+#include <string>
+
+#include "base/callback_forward.h"
+
+class PrefHashFilter;
+
+// Sets up PrefHashFilter::FilterOnLoadInterceptors on |unprotected_pref_filter|
+// and |protected_pref_filter| which prevents each filter from running their on
+// load operations until the interceptors decide to hand the prefs back to them
+// (after migration is complete). |(un)protected_store_cleaner| and
+// |register_on_successful_(un)protected_store_write_callback| are used to do
+// post-migration cleanup tasks. Those should be bound to weak pointers to avoid
+// blocking shutdown. The migration framework is resilient to a failed cleanup
+// (it will simply try again in the next Chrome run).
+void SetupTrackedPreferencesMigration(
+    const std::set<std::string>& unprotected_pref_names,
+    const std::set<std::string>& protected_pref_names,
+    const base::Callback<void(const std::string& key)>&
+        unprotected_store_cleaner,
+    const base::Callback<void(const std::string& key)>& protected_store_cleaner,
+    const base::Callback<void(const base::Closure&)>&
+        register_on_successful_unprotected_store_write_callback,
+    const base::Callback<void(const base::Closure&)>&
+        register_on_successful_protected_store_write_callback,
+    PrefHashFilter* unprotected_pref_hash_filter,
+    PrefHashFilter* protected_pref_hash_filter);
+
+#endif  // CHROME_BROWSER_PREFS_TRACKED_TRACKED_PREFERENCES_MIGRATION_H_