Implemented initial version of server-issued notification client.

chrome/browser/sync/notification_method.h

Index: chrome/browser/sync/notification_method.h
diff --git a/chrome/browser/sync/notification_method.h b/chrome/browser/sync/notification_method.h
index 569f8d25eb5d2ef5ece6dac5e8f96c5ef9ab1729..4e1bcd1682dd9f6ebf8c3fba8b9f6123a03bf12f 100644
--- a/chrome/browser/sync/notification_method.h
+++ b/chrome/browser/sync/notification_method.h
@@ -10,7 +10,7 @@
 namespace browser_sync {
 
 // This is the matrix for the interaction between clients with
-// different notification methods:
+// different notification methods (except for NOTIFICATION_SERVER):
 //
 //          Listen
 //          L T N
@@ -24,6 +24,12 @@ namespace browser_sync {
 // will receive notifications from a client sending with the row
 // notification method. 'E' means means that the notification will be
 // an empty one, which may be dropped by the server in the future.
+//
+// As for NOTIFICATION_SERVER, server-issued notifications will also
+// simulate a peer-issued notification, so that any client with
+// NOTIFICATION_TRANSITIONAL or NOTIFICATION_NEW will be able to
+// receive those, too.  This support will be removed once everyone is
+// on NOTIFICATION_SERVER.
 
 enum NotificationMethod {
   // Old, broken notification method.  Works only if notification
@@ -33,9 +39,17 @@ enum NotificationMethod {
   // notifications if the notification servers don't drop empty
   // notifications.
   NOTIFICATION_TRANSITIONAL,
-  // New, ideal notification method.  Compatible only with
-  // transitional notifications.
+  // New notification method.  Compatible only with transitional
+  // notifications.
+  //
+  // NOTE: "New" is kind of a misnomer, as it refers only to
+  // peer-issued notifications; the plan is to migrate everyone to
+  // using NOTIFICATION_SERVER.
   NOTIFICATION_NEW,
+
+  // Server-issued notifications.  Compatible only with transitional
+  // notifications.
+  NOTIFICATION_SERVER,
 };
 
 extern const NotificationMethod kDefaultNotificationMethod;
@@ -43,8 +57,8 @@ extern const NotificationMethod kDefaultNotificationMethod;
 std::string NotificationMethodToString(
     NotificationMethod notification_method);
 
-// If the given string is not one of "legacy", "transitional", or
-// "new", returns kDefaultNotificationMethod.
+// If the given string is not one of "legacy", "transitional", "new",
+// or "server", returns kDefaultNotificationMethod.
 NotificationMethod StringToNotificationMethod(const std::string& str);
 
 }  // namespace browser_sync