[Sync] Add support for enabling session sync remotely.

chrome/browser/sync/internal_api/sync_manager.h

Index: chrome/browser/sync/internal_api/sync_manager.h
diff --git a/chrome/browser/sync/internal_api/sync_manager.h b/chrome/browser/sync/internal_api/sync_manager.h
index 14350a49748e8a1c08a4bef857406e151c76da4e..dc519b7332a2ac603fe8f3156f8723d84de054a3 100644
--- a/chrome/browser/sync/internal_api/sync_manager.h
+++ b/chrome/browser/sync/internal_api/sync_manager.h
@@ -512,8 +512,14 @@ class SyncManager {
   // only be called after syncapi has been initialized.
   void RefreshEncryption();
 
+  // Gets the set of encrypted types from the cryptographer
+  // Note: opens a transaction.
   syncable::ModelTypeSet GetEncryptedDataTypes() const;
 
+  // Reads the nigori node to determine if session sync should be enabled.
+  // Note: opens a transaction.
+  bool ShouldEnableSessions() const;
+
   // Uses a read-only transaction to determine if the directory being synced has
   // any remaining unsynced items.
   bool HasUnsyncedItems() const;