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

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

Index: third_party/WebKit/Source/core/layout/LayoutBox.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutBox.h b/third_party/WebKit/Source/core/layout/LayoutBox.h
index bc44382b7aaf962239a24deac04d91614ca74f96..2198a02af4e2073799a49719f0cfb9d8c644f4bb 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.h
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.h
@@ -26,6 +26,7 @@
 #include "core/CoreExport.h"
 #include "core/layout/LayoutBoxModelObject.h"
 #include "core/layout/OverflowModel.h"
+#include "core/layout/ScrollEnums.h"
 #include "platform/scroll/ScrollTypes.h"
 #include "platform/scroll/ScrollableArea.h"
 
@@ -42,16 +43,10 @@ enum AvailableLogicalHeightType { ExcludeMarginBorderPadding, IncludeMarginBorde
 // When painting, overlay scrollbars do not take up space and should not affect
 // clipping behavior. During hit testing, overlay scrollbars behave like regular
 // scrollbars and should change how hit testing is clipped.
-enum OverlayScrollbarClipBehavior { IgnoreOverlayScrollbarSize, ExcludeOverlayScrollbarSizeForHitTesting };
 enum MarginDirection { BlockDirection, InlineDirection };
 
 enum ShouldComputePreferred { ComputeActual, ComputePreferred };
 
-enum ScrollOffsetClamping {
-    ScrollOffsetUnclamped,
-    ScrollOffsetClamped
-};
-
 enum ApplyOverflowClipFlag {
     ApplyOverflowClip,
     ApplyNonScrollOverflowClip