Add fast-path for propagated variable changes (WIP)

third_party/WebKit/Source/core/style/ComputedStyle.h

Index: third_party/WebKit/Source/core/style/ComputedStyle.h
diff --git a/third_party/WebKit/Source/core/style/ComputedStyle.h b/third_party/WebKit/Source/core/style/ComputedStyle.h
index 7645fc4d8111f7e6429185ceb5cf62f59f69ead5..32224db9625b9dd2c11d6b3af79f97e6d4d2dbff 100644
--- a/third_party/WebKit/Source/core/style/ComputedStyle.h
+++ b/third_party/WebKit/Source/core/style/ComputedStyle.h
@@ -228,7 +228,8 @@ class CORE_EXPORT ComputedStyle : public ComputedStyleBase,
              (m_rtlOrdering == other.m_rtlOrdering) &&
              (m_printColorAdjust == other.m_printColorAdjust) &&
              (m_insideLink == other.m_insideLink) &&
-             (m_writingMode == other.m_writingMode);
+             (m_writingMode == other.m_writingMode) &&
+             (m_variableReference == other.m_variableReference);
     }
 
     unsigned m_captionSide : 2;        // ECaptionSide
@@ -253,7 +254,10 @@ class CORE_EXPORT ComputedStyle : public ComputedStyleBase,
 
     // CSS Text Layout Module Level 3: Vertical writing support
     unsigned m_writingMode : 2;  // WritingMode
-                                 // 42 bits
+
+    unsigned m_variableReference : 1;  // Whether an inherited property
+                                       // references a variable.
+                                       // 43 bits
   } m_inheritedData;
 
   // don't inherit
@@ -379,6 +383,7 @@ class CORE_EXPORT ComputedStyle : public ComputedStyleBase,
     m_inheritedData.m_pointerEvents = initialPointerEvents();
     m_inheritedData.m_insideLink = NotInsideLink;
     m_inheritedData.m_writingMode = initialWritingMode();
+    m_inheritedData.m_variableReference = false;
 
     m_nonInheritedData.m_effectiveDisplay =
         m_nonInheritedData.m_originalDisplay =
@@ -2650,8 +2655,14 @@ class CORE_EXPORT ComputedStyle : public ComputedStyleBase,
 
   bool inheritedEqual(const ComputedStyle&) const;
   bool nonInheritedEqual(const ComputedStyle&) const;
+
+  // Compares independent inherited properties, not including variables.
   inline bool independentInheritedEqual(const ComputedStyle&) const;
   inline bool nonIndependentInheritedEqual(const ComputedStyle&) const;
+
+  // Compares variables.
+  inline bool variablesEqual(const ComputedStyle&) const;
+
   bool loadingCustomFontsEqual(const ComputedStyle&) const;
   bool inheritedDataShared(const ComputedStyle&) const;
 
@@ -2705,6 +2716,12 @@ class CORE_EXPORT ComputedStyle : public ComputedStyleBase,
   bool hasVariableReferenceFromNonInheritedProperty() const {
     return m_nonInheritedData.m_variableReference;
   }
+  void setHasVariableReferenceFromInheritedProperty() {
+    m_inheritedData.m_variableReference = true;
+  }
+  bool hasVariableReferenceFromInheritedProperty() const {
+    return m_inheritedData.m_variableReference;
+  }
 
   // Animations.
   CSSAnimationData& accessAnimations();