[Sync] Refactor sync manager into interface.

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 de9e00fa12e0b43b0b30b6072fd5c3d2d6db2df5..a49fa6f0f02c1dbd46457634022992d03d1ecfb3 100644
--- a/chrome/browser/sync/profile_sync_service.h
+++ b/chrome/browser/sync/profile_sync_service.h
@@ -34,6 +34,7 @@
 #include "googleurl/src/gurl.h"
 #include "sync/internal_api/public/base/model_type.h"
 #include "sync/internal_api/public/engine/model_safe_worker.h"
+#include "sync/internal_api/public/sync_manager_factory.h"
 #include "sync/internal_api/public/util/experiments.h"
 #include "sync/internal_api/public/util/unrecoverable_error_handler.h"
 #include "sync/js/sync_js_controller.h"
@@ -49,6 +50,7 @@ class ChangeProcessor;
 class DataTypeManager;
 class JsController;
 class SessionModelAssociator;
+
 namespace sessions { class SyncSessionSnapshot; }
 }
 
@@ -792,6 +794,9 @@ class ProfileSyncService : public browser_sync::SyncFrontend,
   // The set of currently enabled sync experiments.
   syncer::Experiments current_experiments;
 
+  // Factory the backend will use to build the SyncManager.
+  syncer::SyncManagerFactory sync_manager_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(ProfileSyncService);
 };