Ignore zero-height fragments during margin collapsing

third_party/WebKit/Source/core/layout/ng/ng_units.cc

Index: third_party/WebKit/Source/core/layout/ng/ng_units.cc
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_units.cc b/third_party/WebKit/Source/core/layout/ng/ng_units.cc
index d65adf7c2a8d0fb29454d3f645e6952a4a783772..bec0be56fa5bf76fa1712c4429e0ff315608a529 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_units.cc
+++ b/third_party/WebKit/Source/core/layout/ng/ng_units.cc
@@ -61,6 +61,16 @@ NGPhysicalOffset NGLogicalOffset::ConvertToPhysical(
   }
 }
 
+bool NGBoxStrut::IsEmpty() const {
+  return *this == NGBoxStrut();
+}
+
+bool NGBoxStrut::operator==(const NGBoxStrut& other) const {
+  return std::tie(other.inline_start, other.inline_end, other.block_start,

[mstensho (USE GERRIT), 2016/09/20 09:59:50]

Wouldn't comparing each of the four members individually be faster than using
std::tie?

[Gleb Lanbin, 2016/09/20 19:18:19]

I didn't test std:tie performance but std::tie is approved to use in Chromium
code https://chromium-cpp.appspot.com/ and it's already used in other parts of
Chromium.

+                  other.block_end) ==
+         std::tie(inline_start, inline_end, block_start, block_end);
+}
+
 void NGMarginStrut::AppendMarginBlockStart(const LayoutUnit& value) {
   if (value < 0) {
     negative_margin_block_start =