Add fast-path for propagated variable changes (WIP)

third_party/WebKit/Source/core/style/StyleRareInheritedData.cpp

Index: third_party/WebKit/Source/core/style/StyleRareInheritedData.cpp
diff --git a/third_party/WebKit/Source/core/style/StyleRareInheritedData.cpp b/third_party/WebKit/Source/core/style/StyleRareInheritedData.cpp
index 0c272d7016e815f950bc14716460eca8196e8540..41dc4e3a326c07d7626310b14c942917ff1d19e1 100644
--- a/third_party/WebKit/Source/core/style/StyleRareInheritedData.cpp
+++ b/third_party/WebKit/Source/core/style/StyleRareInheritedData.cpp
@@ -174,6 +174,11 @@ StyleRareInheritedData::StyleRareInheritedData(const StyleRareInheritedData& o)
 StyleRareInheritedData::~StyleRareInheritedData() {}
 
 bool StyleRareInheritedData::operator==(const StyleRareInheritedData& o) const {
+  return compareEqualVariables(o) && compareEqualNonVariables(o);
+}
+
+bool StyleRareInheritedData::compareEqualNonVariables(
+    const StyleRareInheritedData& o) const {
   return m_textStrokeColor == o.m_textStrokeColor &&
          textStrokeWidth == o.textStrokeWidth &&
          m_textFillColor == o.m_textFillColor &&
@@ -227,10 +232,14 @@ bool StyleRareInheritedData::operator==(const StyleRareInheritedData& o) const {
          m_rubyPosition == o.m_rubyPosition &&
          dataEquivalent(listStyleImage.get(), o.listStyleImage.get()) &&
          dataEquivalent(appliedTextDecorations, o.appliedTextDecorations) &&
-         dataEquivalent(variables, o.variables) &&
          m_textSizeAdjust == o.m_textSizeAdjust;
 }
 
+bool StyleRareInheritedData::compareEqualVariables(
+    const StyleRareInheritedData& o) const {
+  return dataEquivalent(variables, o.variables);
+}
+
 bool StyleRareInheritedData::shadowDataEquivalent(
     const StyleRareInheritedData& o) const {
   return dataEquivalent(textShadow.get(), o.textShadow.get());