Implement 'will-change' parsing

Source/core/rendering/style/RenderStyle.h

Index: Source/core/rendering/style/RenderStyle.h
diff --git a/Source/core/rendering/style/RenderStyle.h b/Source/core/rendering/style/RenderStyle.h
index 147734ead7e4285251dcd487a0cf516d8e3a3942..d3c59cef07dd20da1de97a9f65e16c4d235e6b58 100644
--- a/Source/core/rendering/style/RenderStyle.h
+++ b/Source/core/rendering/style/RenderStyle.h
@@ -53,6 +53,7 @@
 #include "core/rendering/style/StyleSurroundData.h"
 #include "core/rendering/style/StyleTransformData.h"
 #include "core/rendering/style/StyleVisualData.h"
+#include "core/rendering/style/StyleWillChangeData.h"
 #include "core/svg/SVGPaint.h"
 #include "platform/Length.h"
 #include "platform/LengthBox.h"
@@ -953,6 +954,10 @@ public:
 
     ScrollBehavior scrollBehavior() const { return static_cast<ScrollBehavior>(rareNonInheritedData->m_scrollBehavior); }
 
+    const Vector<CSSPropertyID>& willChangeProperties() const { return rareNonInheritedData->m_willChange->m_properties; }
+    bool willChangeContents() const { return rareNonInheritedData->m_willChange->m_contents; }
+    bool willChangeScrollPosition() const { return rareNonInheritedData->m_willChange->m_scrollPosition; }
+
 // attribute setter methods
 
     void setDisplay(EDisplay v) { noninherited_flags._effectiveDisplay = v; }
@@ -1375,6 +1380,10 @@ public:
 
     void setScrollBehavior(ScrollBehavior b) { SET_VAR(rareNonInheritedData, m_scrollBehavior, b); }
 
+    void setWillChangeProperties(const Vector<CSSPropertyID>& properties) { SET_VAR(rareNonInheritedData.access()->m_willChange, m_properties, properties); }

[eseidel, 2014/02/18 23:33:52]

We'll end up copying the vector here.  That's not necessarily bad, but if
rareNonInheritedData isn't sufficiently rare, this could show up on profiles.

+    void setWillChangeContents(bool b) { SET_VAR(rareNonInheritedData.access()->m_willChange, m_contents, b); }
+    void setWillChangeScrollPosition(bool b) { SET_VAR(rareNonInheritedData.access()->m_willChange, m_scrollPosition, b); }
+
     const SVGRenderStyle* svgStyle() const { return m_svgStyle.get(); }
     SVGRenderStyle* accessSVGStyle() { return m_svgStyle.access(); }