sync: Expose ProtocolEvents on ProfileSyncService

Adds code to the sync engine to have it generate protocol events when it
contacts the server.  These events are then sent through the
SyncSession, SyncManager, SyncBackendHostCore, SyncBackendHost, and
finally to the ProfileSyncService.

Objects on the UI thread can register with the ProfileSyncService as
observers of these events, though this CL does not introduce any of
these listeners.

BUG=349301

Review URL: https://codereview.chromium.org/203463005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@258685 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 9 insertions, 0 deletions

diff --git a/components/sync_driver/sync_frontend.h b/components/sync_driver/sync_frontend.h
index f7ed853..47d76be 100644
--- a/components/sync_driver/sync_frontend.h
+++ b/components/sync_driver/sync_frontend.h
@@ -15,6 +15,7 @@
 namespace syncer {
 class DataTypeDebugInfoListener;
 class JsBackend;
+class ProtocolEvent;
 }  // namespace syncer
 
 namespace sync_pb {
@@ -53,6 +54,14 @@ class SyncFrontend {
   // retried.
   virtual void OnSyncConfigureRetry() = 0;
 
+  // Informs the frontned of some network event.  These notifications are
+  // disabled by default and must be enabled through an explicit request to the
+  // SyncBackendHost.
+  //
+  // It's disabld by default to avoid copying data across threads when no one
+  // is listening for it.
+  virtual void OnProtocolEvent(const syncer::ProtocolEvent& event) = 0;
+
   // The status of the connection to the sync server has changed.
   virtual void OnConnectionStatusChange(
       syncer::ConnectionStatus status) = 0;