Use a distinct source parameter on gaia endpoints for the reconcilor.

google_apis/gaia/merge_session_helper.h

Index: google_apis/gaia/merge_session_helper.h
diff --git a/google_apis/gaia/merge_session_helper.h b/google_apis/gaia/merge_session_helper.h
index ff91777cfd001a4b13463cf42cf2c041380f5bf2..ca82643eefd8940664e7c1ad078cdbb42dce4f94 100644
--- a/google_apis/gaia/merge_session_helper.h
+++ b/google_apis/gaia/merge_session_helper.h
@@ -103,6 +103,7 @@ class MergeSessionHelper : public GaiaAuthConsumer,
   };
 
   MergeSessionHelper(OAuth2TokenService* token_service,
+                     const std::string& source,
                      net::URLRequestContextGetter* request_context,
                      Observer* observer);
   virtual ~MergeSessionHelper();
@@ -186,6 +187,9 @@ class MergeSessionHelper : public GaiaAuthConsumer,
   // Makes sure list is empty on destruction.
   ObserverList<Observer, true> observer_list_;
 
+  // Source to use with GAIA endpoints for accounting.
+  std::string source_;
+
   DISALLOW_COPY_AND_ASSIGN(MergeSessionHelper);
 };