Add TypeTraits template for checking safe bitfields (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 a66a3f692703a6fc7afc027125741241d2e39597..b5479148d7196c0cd22f259d9c8497f1637b05f0 100644
--- a/third_party/WebKit/Source/core/style/ComputedStyle.h
+++ b/third_party/WebKit/Source/core/style/ComputedStyle.h
@@ -72,6 +72,7 @@
 #include "wtf/Forward.h"
 #include "wtf/LeakAnnotations.h"
 #include "wtf/RefCounted.h"
+#include "wtf/TypeTraits.h"
 #include "wtf/Vector.h"
 #include <memory>
 
@@ -186,11 +187,13 @@ protected:
 
         bool operator!=(const InheritedData& other) const { return !(*this == other); }
 
+        static_assert(IsEnumSafeToStoreInBitfield<EVisibility>::value, "EVisibility is stored in a bitfield on ComputedStyle");
+
         unsigned m_emptyCells : 1; // EEmptyCells
         unsigned m_captionSide : 2; // ECaptionSide
         unsigned m_listStyleType : 7; // EListStyleType
         unsigned m_listStylePosition : 1; // EListStylePosition
-        unsigned m_visibility : 2; // EVisibility
+        EVisibility m_visibility : 2;
         unsigned m_textAlign : 4; // ETextAlign
         unsigned m_textTransform : 2; // ETextTransform
         unsigned m_textUnderline : 1;
@@ -298,7 +301,7 @@ protected:
         m_inheritedData.m_captionSide = initialCaptionSide();
         m_inheritedData.m_listStyleType = initialListStyleType();
         m_inheritedData.m_listStylePosition = initialListStylePosition();
-        m_inheritedData.m_visibility = static_cast<unsigned>(initialVisibility());
+        m_inheritedData.m_visibility = initialVisibility();
         m_inheritedData.m_textAlign = initialTextAlign();
         m_inheritedData.m_textTransform = initialTextTransform();
         m_inheritedData.m_textUnderline = false;
@@ -1470,7 +1473,7 @@ public:
     // visibility
     static EVisibility initialVisibility() { return EVisibility::Visible; }
     EVisibility visibility() const { return static_cast<EVisibility>(m_inheritedData.m_visibility); }
-    void setVisibility(EVisibility v) { m_inheritedData.m_visibility = static_cast<unsigned>(v); }
+    void setVisibility(EVisibility v) { m_inheritedData.m_visibility = v; }
 
     // white-space inherited
     static EWhiteSpace initialWhiteSpace() { return NORMAL; }