Move SelectionState out of LayoutObject and into Line Layout API

Source/core/layout/api/SelectionState.h

+// Copyright 2015 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 SelectionState_h
+#define SelectionState_h
+
+namespace blink {
+
+enum SelectionState {
+    SelectionNone, // The object is not selected.
+    SelectionStart, // The object either contains the start of a selection run or is the start of a run.
+    SelectionInside, // The object is fully encompassed by a selection run.
+    SelectionEnd, // The object either contains the end of a selection run or is the end of a run.
+    SelectionBoth // The object contains an entire run or is the sole selected object in that run.
+};
+
+} // namespace blink
+
+#endif // SelectionState_h