Optimize collapsed border calculation (step 1)

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

Index: third_party/WebKit/Source/core/layout/LayoutTable.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutTable.h b/third_party/WebKit/Source/core/layout/LayoutTable.h
index a803b6f9efd7f44136230548ae6626e9e9b9c967..a6ea41f20895f1e328198d7bcf213fbf4f82e08e 100644
--- a/third_party/WebKit/Source/core/layout/LayoutTable.h
+++ b/third_party/WebKit/Source/core/layout/LayoutTable.h
@@ -416,6 +416,7 @@ class CORE_EXPORT LayoutTable final : public LayoutBlock {
     return collapsed_borders_;
   }
   void InvalidateCollapsedBorders();
+  void InvalidateCollapsedBordersForAllCellsIfNeeded();

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

nit: believe we're not using 'IfNeeded' suffix any more as it's usually
implicit.

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

This "IfNeeded" is meaningful because the function invalidate all cells only if
needs_invalidate_collapsed_borders_for_all_cells_ is true. Removing "IfNeeded"
will imply we always invalidate all cells which is totally different from what
the function will do.

[wkorman, 2017/04/28 21:40:15]

Am fine with this.

But for general discussion, I think this is debatable. We have dirty flags for
many things, and we have methods that only enact logic if/when/until the flag is
set, and not all of those methods are named IfNeeded.

Maybe you are proposing, if methods give explicit consideration to dirty state
that is itself named need_xxx, then it is worth naming methods with IfNeeded
suffix?

But, today it seems that it is often implicit that the method will try to be
smart, and the manner in which it is smart can be opaque to external callers.

See for example the names of a wide range of methods with early-outs in
LayoutObject (search for "return;")

Or, the many paint invalidation flags on LayoutObject checked in Invalidator
methods that always enact some logic. PaintInvalidator::InvalidatePaint always
calls UpdatePaintingLayer, but conditionally does other logic, bailing on
!object.ShouldCheckForPaintInvalidation or
!(context.forced_subtree_invalidation_flags &
~PaintInvalidatorContext::kForcedSubtreeVisualRectUpdate).

 
   bool HasSections() const { return Header() || Footer() || FirstBody(); }
 
@@ -588,6 +589,7 @@ class CORE_EXPORT LayoutTable final : public LayoutBlock {
   // field.
   CollapsedBorderValues collapsed_borders_;
   bool collapsed_borders_valid_ : 1;
+  bool needs_invalidate_collapsed_borders_for_all_cells_ : 1;
 
   mutable bool has_col_elements_ : 1;
   mutable bool needs_section_recalc_ : 1;