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

chrome/browser/sync/profile_sync_service.h

Index: chrome/browser/sync/profile_sync_service.h
diff --git a/chrome/browser/sync/profile_sync_service.h b/chrome/browser/sync/profile_sync_service.h
index 3a779ba20e6402ecb872df561a6156887177f8d2..7b2712046a0ec5c4c7b135d17a4af273c34d9a45 100644
--- a/chrome/browser/sync/profile_sync_service.h
+++ b/chrome/browser/sync/profile_sync_service.h
@@ -35,6 +35,7 @@
 #include "sync/engine/model_safe_worker.h"
 #include "sync/js/sync_js_controller.h"
 #include "sync/syncable/model_type.h"
+#include "sync/util/sync_experiments.h"
 #include "sync/util/unrecoverable_error_handler.h"
 
 class Profile;
@@ -235,8 +236,8 @@ class ProfileSyncService : public browser_sync::SyncFrontend,
   virtual void OnEncryptionComplete() OVERRIDE;
   virtual void OnMigrationNeededForTypes(
       syncable::ModelTypeSet types) OVERRIDE;
-  virtual void OnDataTypesChanged(
-      syncable::ModelTypeSet to_add) OVERRIDE;
+  virtual void OnExperimentsChanged(
+      const browser_sync::SyncExperiments& experiments) OVERRIDE;
   virtual void OnActionableError(
       const browser_sync::SyncProtocolError& error) OVERRIDE;
 
@@ -745,6 +746,9 @@ class ProfileSyncService : public browser_sync::SyncFrontend,
   // data types.
   bool setup_in_progress_;
 
+  // The set of currently enabled sync experiments.
+  browser_sync::SyncExperiments current_experiments;
+
   DISALLOW_COPY_AND_ASSIGN(ProfileSyncService);
 };