[Sync] Add support for automatic enabling of syncing tab favicons.

sync/util/experiments.h

Index: sync/util/experiments.h
diff --git a/sync/util/experiments.h b/sync/util/experiments.h
new file mode 100644
index 0000000000000000000000000000000000000000..7cd77af17898f406d62efd11536b188dd42c8d8b
--- /dev/null
+++ b/sync/util/experiments.h
@@ -0,0 +1,32 @@
+// 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.
+
+#ifndef SYNC_UTIL_EXPERIMENTS_
+#define SYNC_UTIL_EXPERIMENTS_
+#pragma once
+
+#include "sync/syncable/model_type.h"
+
+namespace browser_sync {
+
+// A structure to hold the enable status of experimental sync features.
+struct Experiments {
+  Experiments() : sync_tabs(false), sync_tab_favicons(false) {}
+
+  bool Matches(const Experiments& rhs) {
+    return (sync_tabs == rhs.sync_tabs) &&
+           (sync_tab_favicons == rhs.sync_tab_favicons);
+  }
+
+  // Enable the tab sync (SESSIONS) datatype.
+  bool sync_tabs;
+
+  // Enable syncing of favicons within tab sync (only has an effect if tab sync
+  // is already enabled). This takes effect on the next restart.
+  bool sync_tab_favicons;
+};
+
+}
+
+#endif  // SYNC_UTIL_EXPERIMENTS_