Add SyncAuthProvider interface and implementation

sync/internal_api/public/sync_auth_provider.h

Index: sync/internal_api/public/sync_auth_provider.h
diff --git a/sync/internal_api/public/sync_auth_provider.h b/sync/internal_api/public/sync_auth_provider.h
new file mode 100644
index 0000000000000000000000000000000000000000..77980ba33b2672c28b3d1d4fc97d1c2b1a2c9de3
--- /dev/null
+++ b/sync/internal_api/public/sync_auth_provider.h
@@ -0,0 +1,33 @@
+// Copyright 2014 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_INTERNAL_API_PUBLIC_SYNC_AUTH_PROVIDER_H_
+#define SYNC_INTERNAL_API_PUBLIC_SYNC_AUTH_PROVIDER_H_
+
+#include "base/callback.h"
+
+class GoogleServiceAuthError;
+
+namespace syncer {
+
+// SyncAuthProvider is interface to access token related functions from sync
+// engine.
+class SyncAuthProvider {
+ public:
+  typedef base::Callback<void(const GoogleServiceAuthError& error,
+                              const std::string& token)> RequestTokenCallback;
+
+  virtual ~SyncAuthProvider() {}
+
+  // Request access token for sync. Callback will be called with error and
+  // access token. If error is anything other than NONE then token is invalid.
+  virtual void RequestAccessToken(const RequestTokenCallback& callback) = 0;
+
+  // Invalidate access token that was rejected by sync server.
+  virtual void InvalidateAccessToken(const std::string& token) = 0;
+};
+
+}  // namespace syncer
+
+#endif  // SYNC_INTERNAL_API_PUBLIC_SYNC_AUTH_PROVIDER_H_