Show custom properties in the computed style pane of the inspector.

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

 #ifndef StyleVariableData_h
 #define StyleVariableData_h
 
 #include "core/css/CSSVariableData.h"
 #include "wtf/Forward.h"
 #include "wtf/HashMap.h"
 #include "wtf/RefCounted.h"
 #include "wtf/text/AtomicStringHash.h"
 
 namespace blink {
 
 class StyleVariableData : public RefCounted<StyleVariableData> {
 public:
     static PassRefPtr<StyleVariableData> create() { return adoptRef(new StyleVariableData()); }
     PassRefPtr<StyleVariableData> copy() const { return adoptRef(new StyleVariableData(*this)); }
 
     bool operator==(const StyleVariableData& other) const { return other.m_data == m_data; }
     bool operator!=(const StyleVariableData& other) const { return !(*this == other); }
 
     void setVariable(const AtomicString& name, PassRefPtr<CSSVariableData> value) { m_data.set(name, value); }
     CSSVariableData* getVariable(const AtomicString& name) const { return m_data.get(name); }
     void removeVariable(const AtomicString& name) { return m_data.remove(name); }
+
+    const HashMap<AtomicString, RefPtr<CSSVariableData>>* getVariables() const { return &m_data; }
 private:
     StyleVariableData() = default;
     StyleVariableData(const StyleVariableData& other) : RefCounted<StyleVariableData>(), m_data(other.m_data) { }
 
     friend class CSSVariableResolver;
 
     HashMap<AtomicString, RefPtr<CSSVariableData>> m_data;
 };
 
 } // namespace blink
 
 #endif // StyleVariableData_h