[Sync] Convert SyncSessionSnapshot to a copy-able class.

sync/engine/sync_engine_event.h

Index: sync/engine/sync_engine_event.h
diff --git a/sync/engine/sync_engine_event.h b/sync/engine/sync_engine_event.h
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+++ b/sync/engine/sync_engine_event.h
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+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SYNC_ENGINE_SYNC_ENGINE_EVENT_H_
+#define SYNC_ENGINE_SYNC_ENGINE_EVENT_H_
+#pragma once
+
+#include <string>
+
+#include "base/observer_list.h"
+#include "sync/sessions/session_state.h"
+#include "sync/syncable/model_type.h"
+
+namespace syncable {
+class Id;
+}
+
+namespace browser_sync {
+
+struct SyncEngineEvent {
+  enum EventCause {
+    ////////////////////////////////////////////////////////////////
+    // Sent on entry of Syncer state machine
+    SYNC_CYCLE_BEGIN,
+
+    // SyncerCommand generated events.
+    STATUS_CHANGED,
+
+    // We have reached the SYNCER_END state in the main sync loop.
+    SYNC_CYCLE_ENDED,
+
+    ////////////////////////////////////////////////////////////////
+    // Generated in response to specific protocol actions or events.
+
+    // New token in updated_token.
+    UPDATED_TOKEN,
+
+    // This is sent after the Syncer (and SyncerThread) have initiated self
+    // halt due to no longer being permitted to communicate with the server.
+    // The listener should sever the sync / browser connections and delete sync
+    // data (i.e. as if the user clicked 'Stop Syncing' in the browser.
+    STOP_SYNCING_PERMANENTLY,
+
+    // These events are sent to indicate when we know the clearing of
+    // server data have failed or succeeded.
+    CLEAR_SERVER_DATA_SUCCEEDED,
+    CLEAR_SERVER_DATA_FAILED,
+
+    // This event is sent when we receive an actionable error. It is upto
+    // the listeners to figure out the action to take using the snapshot sent.
+    ACTIONABLE_ERROR,
+  };
+
+  explicit SyncEngineEvent(EventCause cause);
+  ~SyncEngineEvent();
+
+  EventCause what_happened;
+
+  // The last session used for syncing.
+  sessions::SyncSessionSnapshot snapshot;
+
+  // Update-Client-Auth returns a new token for sync use.
+  std::string updated_token;
+};
+
+class SyncEngineEventListener {
+ public:
+  // TODO(tim): Consider splitting this up to multiple callbacks, rather than
+  // have to do Event e(type); OnSyncEngineEvent(e); at all callsites,
+  virtual void OnSyncEngineEvent(const SyncEngineEvent& event) = 0;
+ protected:
+  virtual ~SyncEngineEventListener() {}
+};
+
+}  // namespace browser_sync
+
+#endif  // SYNC_ENGINE_SYNC_ENGINE_EVENT_H_