Issue #1355 - Better way to create display items for column backgrounds

Part 1: Remove current table item, as it's never set.

Part 2: Get rid of generic table painting code, and handle each class separately.

Part 4: Hoist outline skipping into col(group) frame code.

Part 5: Skip box-shadow for table column and column groups.

Part 6: Store column and column group backgrounds separately, and then append them before the rest of the table contents.

Part 7: Pass rects in display list coordinates to AppendBackgroundItemsToTop.

Part 8: Create column and column group background display items as part of the cell's BuildDisplayList.

Part 9: Used cached values instead of calling nsDisplayListBuilder::ToReferenceFrame when possible, since it can be expensive when the requested frame isn't the builder's current frame.

Part 10: Make sure we build display items for table parts where only the normal position is visible, since we may need to create background items for ancestors at that position.

Part 11: Create an AutoBuildingDisplayList when we create background items for table columns and column groups, so that we initialize the invalidation state correctly.

1 files changed, 7 insertions, 1 deletions

diff --git a/layout/tables/nsTableColFrame.cpp b/layout/tables/nsTableColFrame.cpp
index 659f0fd35..6723f4701 100644
--- a/layout/tables/nsTableColFrame.cpp
+++ b/layout/tables/nsTableColFrame.cpp
@@ -112,7 +112,13 @@ void
 nsTableColFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
                                   const nsDisplayListSet& aLists)
 {
-  nsTableFrame::DisplayGenericTablePart(aBuilder, this, aLists);
+  // Per https://drafts.csswg.org/css-tables-3/#global-style-overrides:
+  // "All css properties of table-column and table-column-group boxes are
+  // ignored, except when explicitly specified by this specification."
+  // CSS outlines and box-shadows fall into this category, so we skip them
+  // on these boxes.
+
+  MOZ_ASSERT_UNREACHABLE("Cols don't paint themselves");
 }
 
 int32_t nsTableColFrame::GetSpan()