Add ScrollEnums.h, so that PaintLayerScrollableArea.h doesn't have to include LayoutBox.h

third_party/WebKit/Source/core/layout/ScrollEnums.h

Index: third_party/WebKit/Source/core/layout/ScrollEnums.h
diff --git a/third_party/WebKit/Source/core/layout/ScrollEnums.h b/third_party/WebKit/Source/core/layout/ScrollEnums.h
new file mode 100644
index 0000000000000000000000000000000000000000..300ab3d8b9c48c1b64274c54f9bc48f1abefedf3
--- /dev/null
+++ b/third_party/WebKit/Source/core/layout/ScrollEnums.h
@@ -0,0 +1,18 @@
+// Copyright 2016 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 ScrollEnums_h
+#define ScrollEnums_h
+
+enum OverlayScrollbarClipBehavior {
+    IgnoreOverlayScrollbarSize,
+    ExcludeOverlayScrollbarSizeForHitTesting
+};
+
+enum ScrollOffsetClamping {
+    ScrollOffsetUnclamped,
+    ScrollOffsetClamped
+};
+
+#endif // ScrollEnums_h