Optimize collapsed border calculation (step 1)

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

Index: third_party/WebKit/Source/core/layout/LayoutTable.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutTable.cpp b/third_party/WebKit/Source/core/layout/LayoutTable.cpp
index b5f782ce7e5ea2ea7db8a03b16dbb4fa1a97e6dc..c0bb217186c7c7920a379781fad95237bbd71264 100644
--- a/third_party/WebKit/Source/core/layout/LayoutTable.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutTable.cpp
@@ -58,6 +58,7 @@ LayoutTable::LayoutTable(Element* element)
       foot_(nullptr),
       first_body_(nullptr),
       collapsed_borders_valid_(false),
+      needs_invalidate_collapsed_borders_for_all_cells_(false),
       has_col_elements_(false),
       needs_section_recalc_(false),
       column_logical_width_changed_(false),
@@ -780,9 +781,32 @@ void LayoutTable::UpdateLayout() {
 void LayoutTable::InvalidateCollapsedBorders() {
   collapsed_borders_.clear();
   collapsed_borders_valid_ = false;
+  needs_invalidate_collapsed_borders_for_all_cells_ = true;
   SetMayNeedPaintInvalidation();
 }
 
+void LayoutTable::InvalidateCollapsedBordersForAllCellsIfNeeded() {
+  DCHECK(CollapseBorders());

[wkorman, 2017/04/27 20:11:15]

I was briefly confused with this vs. CollapsedBorders(). We should revise one or
the other method name to make clearer the difference (former checks whether
style is set, latter returns the collapsed border values instance, and differ by
only one char amidst name).

[Xianzhu, 2017/04/28 20:31:44]

Created https://codereview.chromium.org/2850633003/ to rename it.

+
+  if (!needs_invalidate_collapsed_borders_for_all_cells_)
+    return;
+  needs_invalidate_collapsed_borders_for_all_cells_ = false;
+
+  for (LayoutObject* section = FirstChild(); section;
+       section = section->NextSibling()) {
+    if (!section->IsTableSection())
+      continue;
+    for (LayoutTableRow* row = ToLayoutTableSection(section)->FirstRow(); row;
+         row = row->NextRow()) {
+      for (LayoutTableCell* cell = row->FirstCell(); cell;
+           cell = cell->NextCell()) {
+        DCHECK_EQ(cell->Table(), this);
+        cell->InvalidateCollapsedBorderValues();
+      }
+    }
+  }
+}
+
 // Collect all the unique border values that we want to paint in a sorted list.
 // During the collection, each cell saves its recalculated borders into the
 // cache of its containing section, and invalidates itself if any border