Improve comment in OAuth2TokenServiceRequest::Core.

google_apis/gaia/oauth2_token_service_request.cc

Index: google_apis/gaia/oauth2_token_service_request.cc
diff --git a/google_apis/gaia/oauth2_token_service_request.cc b/google_apis/gaia/oauth2_token_service_request.cc
index b652c2b26c1e5f75798a96ed9e6481852d80e4ec..0c737ad5ce4a0739455f0d3750dd4f126a17b6d0 100644
--- a/google_apis/gaia/oauth2_token_service_request.cc
+++ b/google_apis/gaia/oauth2_token_service_request.cc
@@ -77,8 +77,9 @@ class OAuth2TokenServiceRequest::Core
   scoped_refptr<base::SingleThreadTaskRunner> token_service_task_runner_;
   OAuth2TokenServiceRequest* owner_;
 
-  // It is important that provider_ is destroyed on the owner thread, not the
-  // token_service_task_runner_ thread.
+  // Clear on owner thread.  OAuth2TokenServiceRequest promises to clear its
+  // last reference to TokenServiceProvider on the owner thread so the caller
+  // can ensure it is destroyed on the owner thread if desired.
   scoped_refptr<TokenServiceProvider> provider_;
 
   DISALLOW_COPY_AND_ASSIGN(Core);