Synchronize new proto changes.
diff --git a/google/spanner/v1/spanner.proto b/google/spanner/v1/spanner.proto
index 0e51e82..95d3154 100644
--- a/google/spanner/v1/spanner.proto
+++ b/google/spanner/v1/spanner.proto
@@ -172,7 +172,8 @@
 
 // A session in the Cloud Spanner API.
 message Session {
-  // The name of the session.
+  // The name of the session. This is always system-assigned; values provided
+  // when creating a session are ignored.
   string name = 1;
 
   // The labels for the session.