Make sure ImmutableStylePropertySet uses the new 16 bits size of StylePropertyMetadata.

Source/core/css/CSSProperty.h

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006 Apple Computer, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 23 matching lines @@
     StylePropertyMetadata(CSSPropertyID propertyID, bool isSetFromShorthand, int indexInShorthandsVector, bool important, bool implicit, bool inherited)
         : m_propertyID(propertyID)
         , m_isSetFromShorthand(isSetFromShorthand)
         , m_indexInShorthandsVector(indexInShorthandsVector)
         , m_important(important)
         , m_implicit(implicit)
         , m_inherited(inherited)
     {
     }
 
+    StylePropertyMetadata(uint32_t data)
+    {
+        memcpy(this, &data, sizeof(StylePropertyMetadata));

[Jeffrey Yasskin, 2013/06/21 19:56:27]

memcpy is dangerous because of endian-ness issues, so either be sure to test
this on a big-endian machine (to be sure that data is always an in-memory value)
or do the shifting yourself in this constructor.

+    }
+
     CSSPropertyID shorthandID() const;
 
     unsigned m_propertyID : 10;

[Jeffrey Yasskin, 2013/06/21 19:56:27]

If you change the type of these fields to uint16_t, that should reduce
sizeof(StylePropertyMetadata) to 2 on x86, and probably on all 8-bit-byte
architectures. (Inferring from "bit-fields must be contained in a storage unit
appropriate for its declared type" in the AMD64 ABI v0.99, which I can't find on
the internet anymore. :( )

This probably obviates the rest of the CL, but I've left my C++-correctness
comments anyway.

     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, bool isSetFromShorthand = false, int indexInShorthandsVector = 0, bool implicit = false)
@@ skipping 77 matching lines @@
 } // namespace WebCore
 
 namespace WTF {
 template <> struct VectorTraits<WebCore::CSSProperty> : VectorTraitsBase<false, WebCore::CSSProperty> {
     static const bool canInitializeWithMemset = true;
     static const bool canMoveWithMemcpy = true;
 };
 }
 
 #endif // CSSProperty_h