Revert of Paint collapsed borders of a table as one display item

third_party/WebKit/Source/platform/graphics/paint/DisplayItem.h

Index: third_party/WebKit/Source/platform/graphics/paint/DisplayItem.h
diff --git a/third_party/WebKit/Source/platform/graphics/paint/DisplayItem.h b/third_party/WebKit/Source/platform/graphics/paint/DisplayItem.h
index efdf25d6206f9d9e05bb5fbebceb40010d1eec51..90d9449e1ac54dc86e2d5070de0884c9a59216d2 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/DisplayItem.h
+++ b/third_party/WebKit/Source/platform/graphics/paint/DisplayItem.h
@@ -110,7 +110,15 @@
     kTableCellBackgroundFromColumn,
     kTableCellBackgroundFromSection,
     kTableCellBackgroundFromRow,
-    kTableCollapsedBorders,
+    // Table collapsed borders can be painted together (e.g., left & top) but
+    // there are at most 4 phases of collapsed border painting for a single
+    // cell. To disambiguate these phases of collapsed border painting, a mask
+    // is used. TableCollapsedBorderBase can be larger than
+    // TableCollapsedBorderUnalignedBase to ensure the base lower bits are 0's.
+    kTableCollapsedBorderUnalignedBase,
+    kTableCollapsedBorderBase =
+        (((kTableCollapsedBorderUnalignedBase - 1) >> 4) + 1) << 4,
+    kTableCollapsedBorderLast = kTableCollapsedBorderBase + 0x0f,
     kTableSectionBoxShadowInset,
     kTableSectionBoxShadowNormal,
     kTableRowBoxShadowInset,
@@ -194,6 +202,19 @@
     kTypeLast = kUninitializedType
   };
 
+  static_assert(kTableCollapsedBorderBase >= kTableCollapsedBorderUnalignedBase,
+                "TableCollapsedBorder types overlap with other types");
+  static_assert((kTableCollapsedBorderBase & 0xf) == 0,
+                "The lowest 4 bits of TableCollapsedBorderBase should be zero");
+  // Bits or'ed onto TableCollapsedBorderBase to generate a real table collapsed
+  // border type.
+  enum TableCollapsedBorderSides {
+    TableCollapsedBorderTop = 1 << 0,
+    TableCollapsedBorderRight = 1 << 1,
+    TableCollapsedBorderBottom = 1 << 2,
+    TableCollapsedBorderLeft = 1 << 3,
+  };
+
   DisplayItem(const DisplayItemClient& client, Type type, size_t derivedSize)
       : m_client(&client),
         m_type(type),