Don't always invalidate collapsed borders during table layout

third_party/WebKit/Source/core/layout/LayoutTableRow.cpp

Index: third_party/WebKit/Source/core/layout/LayoutTableRow.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutTableRow.cpp b/third_party/WebKit/Source/core/layout/LayoutTableRow.cpp
index 60a3c3f2bd44ae491f482cf93d7c3b0f12028655..b18c797e6ed844e346b6d23b586ab4efcc5706b2 100644
--- a/third_party/WebKit/Source/core/layout/LayoutTableRow.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutTableRow.cpp
@@ -172,6 +172,7 @@ void LayoutTableRow::AddChild(LayoutObject* child, LayoutObject* before_child) {
     // neighboring cells.
     LayoutTable* enclosing_table = Table();
     if (enclosing_table && enclosing_table->CollapseBorders()) {
+      enclosing_table->InvalidateCollapsedBorders();

[wkorman, 2017/04/26 23:57:35]

Would we consider further optimizing this case? We invalidate the whole table
but we may only need to actually invalidate a portion of it.

Asking because, if the answer is perhaps down the line, then we should add a
TODO comment. If not, no worries.

[Xianzhu, 2017/04/27 15:43:40]

This marks the table's collapsed borders data structure dirty, and later we'll
update it. In next steps (https://codereview.chromium.org/2805103003/), update
of collapsed borders will be incremental with invalidation flag per cell, but
here we still need to invalidate the table collapsed borders here.

       if (LayoutTableCell* previous_cell = cell->PreviousCell())
         previous_cell->SetNeedsLayoutAndPrefWidthsRecalc(
             LayoutInvalidationReason::kTableChanged);