Reduce CSSProperty's StylePropertyMetadata memory footprint by half when used inside a ImmutableSty…

Source/core/css/CSSProperty.h

Index: Source/core/css/CSSProperty.h
diff --git a/Source/core/css/CSSProperty.h b/Source/core/css/CSSProperty.h
index 7b508141c6ff725071eda61793a030322a3a8583..1435888635b251d74e5d4a5bf8c904774260b070 100644
--- a/Source/core/css/CSSProperty.h
+++ b/Source/core/css/CSSProperty.h
@@ -26,35 +26,36 @@
 #include "core/platform/text/TextDirection.h"
 #include "core/platform/text/WritingMode.h"
 #include "core/rendering/style/RenderStyleConstants.h"
-#include <wtf/PassRefPtr.h>
-#include <wtf/RefPtr.h>
+#include "wtf/PassRefPtr.h"
+#include "wtf/RefPtr.h"
 
 namespace WebCore {
 
-union StylePropertyMetadata {
-    StylePropertyMetadata(CSSPropertyID propertyID, CSSPropertyID shorthandID, bool important, bool implicit, bool inherited)
+struct StylePropertyMetadata {
+    StylePropertyMetadata(CSSPropertyID propertyID, bool isSetFromShorthand, int indexInShorthandsVector, bool important, bool implicit, bool inherited)
         : m_propertyID(propertyID)
-        , m_shorthandID(shorthandID)
+        , m_isSetFromShorthand(isSetFromShorthand)
+        , m_indexInShorthandsVector(indexInShorthandsVector)
         , m_important(important)
         , m_implicit(implicit)
         , m_inherited(inherited)
     {
     }
 
-    unsigned m_bits;
-    struct {
-        unsigned m_propertyID : 14;
-        unsigned m_shorthandID : 14; // If this property was set as part of a shorthand, gives the shorthand.
-        unsigned m_important : 1;
-        unsigned m_implicit : 1; // Whether or not the property was set implicitly as the result of a shorthand.
-        unsigned m_inherited : 1;
-    };
+    CSSPropertyID shorthandID() const;
+
+    unsigned m_propertyID : 10;
+    unsigned m_isSetFromShorthand : 1;
+    unsigned m_indexInShorthandsVector : 2; // If this property was set as part of an ambiguous shorthand, gives the index in the shorthands vector.
+    unsigned m_important : 1;
+    unsigned m_implicit : 1; // Whether or not the property was set implicitly as the result of a shorthand.
+    unsigned m_inherited : 1;
 };
 
 class CSSProperty {
 public:
-    CSSProperty(CSSPropertyID propertyID, PassRefPtr<CSSValue> value, bool important = false, CSSPropertyID shorthandID = CSSPropertyInvalid, bool implicit = false)
-        : m_metadata(propertyID, shorthandID, important, implicit, isInheritedProperty(propertyID))
+    CSSProperty(CSSPropertyID propertyID, PassRefPtr<CSSValue> value, bool important = false, bool isSetFromShorthand = false, int indexInShorthandsVector = 0, bool implicit = false)
+        : m_metadata(propertyID, isSetFromShorthand, indexInShorthandsVector, important, implicit, isInheritedProperty(propertyID))
         , m_value(value)
     {
     ASSERT((propertyID == CSSPropertyVariable) == (m_value && m_value->isVariableValue()));
@@ -69,7 +70,8 @@ public:
     }
 
     CSSPropertyID id() const { return static_cast<CSSPropertyID>(m_metadata.m_propertyID); }
-    CSSPropertyID shorthandID() const { return static_cast<CSSPropertyID>(m_metadata.m_shorthandID); }
+    bool isSetFromShorthand() const { return m_metadata.m_isSetFromShorthand; };
+    CSSPropertyID shorthandID() const { return m_metadata.shorthandID(); };
     bool isImportant() const { return m_metadata.m_important; }
 
     CSSValue* value() const { return m_value.get(); }