Add a WebLockOrientationError independant from WebLockOrientationCallback.

public/platform/WebLockOrientationError.h

+// 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 WebLockOrientationError_h
+#define WebLockOrientationError_h
+
+namespace blink {
+
+enum WebLockOrientationError {
+    // If locking isn't available on the platform.
+    WebLockOrientationErrorNotAvailable,
+
+    // If fullscreen is required to lock.
+    WebLockOrientationErrorFullScreenRequired,
+
+    // If another lock/unlock got called before that one ended.
+    WebLockOrientationErrorCanceled,
+};
+
+} // namespace blink
+
+#endif // WebLockOrientationError_h