Adding or changing any of box-shadow, outline, or border-image-outset does not need a layout..

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

Index: third_party/WebKit/Source/core/style/StyleDifference.h
diff --git a/third_party/WebKit/Source/core/style/StyleDifference.h b/third_party/WebKit/Source/core/style/StyleDifference.h
index 360642f7a45780e0f369111b07e80fcb8d5ee213..ca1d634ecffb56d3c52b721d75359bbca44e4a29 100644
--- a/third_party/WebKit/Source/core/style/StyleDifference.h
+++ b/third_party/WebKit/Source/core/style/StyleDifference.h
@@ -27,6 +27,7 @@ public:
     StyleDifference()
         : m_paintInvalidationType(NoPaintInvalidation)
         , m_layoutType(NoLayout)
+        , m_recomputeOverflow(NoRecomputeFlow)
         , m_propertySpecificDifferences(0)
     { }
 
@@ -66,6 +67,9 @@ public:
     bool needsFullLayout() const { return m_layoutType == FullLayout; }
     void setNeedsFullLayout() { m_layoutType = FullLayout; }
 
+    bool needsRecomputeOverflow() const { return m_recomputeOverflow == RecomputeOverflow; }
+    void setNeedsRecomputeOverflow() { m_recomputeOverflow = RecomputeOverflow; }
+
     bool transformChanged() const { return m_propertySpecificDifferences & TransformChanged; }
     void setTransformChanged() { m_propertySpecificDifferences |= TransformChanged; }
 
@@ -99,6 +103,12 @@ private:
     };
     unsigned m_layoutType : 2;
 
+    enum RecomputeOverflowType {

[Xianzhu, 2016/04/15 04:59:16]

We don't need to define a private enum to replace a bool like this. Using bool
in the getter and setter is already clear enough.

(We do prefer enum to bool for function parameters where the meaning of
true/false is not clear at call sites.)

[rhogan, 2016/04/15 19:34:32]

Sounds good.

+        NoRecomputeFlow = 0,
+        RecomputeOverflow
+    };
+    unsigned m_recomputeOverflow : 1;
+
     unsigned m_propertySpecificDifferences : 6;
 };