Clean up PageBoundaryRule enum.

Source/core/layout/LayoutMultiColumnSet.cpp

Index: Source/core/layout/LayoutMultiColumnSet.cpp
diff --git a/Source/core/layout/LayoutMultiColumnSet.cpp b/Source/core/layout/LayoutMultiColumnSet.cpp
index cb8af42fed9426c4665a459190ba14dbd35e1131..530b05756fee50522dbd041c8ed95164241bacb0 100644
--- a/Source/core/layout/LayoutMultiColumnSet.cpp
+++ b/Source/core/layout/LayoutMultiColumnSet.cpp
@@ -81,9 +81,10 @@ LayoutUnit LayoutMultiColumnSet::pageRemainingLogicalHeightForOffset(LayoutUnit
     LayoutUnit pageLogicalBottom = row.columnLogicalTopForOffset(offsetInFlowThread) + pageLogicalHeight;
     LayoutUnit remainingLogicalHeight = pageLogicalBottom - offsetInFlowThread;
 
-    if (pageBoundaryRule == IncludePageBoundary) {
-        // If IncludePageBoundary is set, the line exactly on the top edge of a
-        // column will act as being part of the previous column.
+    if (pageBoundaryRule == AssociateWithFormerPage) {
+        // An offset exactly at a column boundary will act as being part of the former column in
+        // question (i.e. no remaining space), rather than being part of the latter (i.e. one whole
+        // column length of remaining space).
         remainingLogicalHeight = intMod(remainingLogicalHeight, pageLogicalHeight);
     }
     return remainingLogicalHeight;