Clear StyleResolverState after each resolve.

Source/core/css/resolver/StyleResolverState.h

Index: Source/core/css/resolver/StyleResolverState.h
diff --git a/Source/core/css/resolver/StyleResolverState.h b/Source/core/css/resolver/StyleResolverState.h
index b8bb0368bc0e9d502caab302da68ab5ccf15caa0..e04ed7a3d084d161d5f85cf66cbb408f7312f994 100644
--- a/Source/core/css/resolver/StyleResolverState.h
+++ b/Source/core/css/resolver/StyleResolverState.h
@@ -82,6 +82,15 @@ private:
     bool m_resetStyleInheritance;
 };
 
+// Initializes a StyleResolverState within a scope.
+class ScopedStyleResolution {

[Jeffrey Yasskin, 2013/07/12 19:58:27]

In a subsequent change, we could remove this entirely, in favor of constructing
a new StyleResolverState on the stack for each resolution and storing a pointer
to it in m_state. I don't want to do that in this change because it could have
performance implications (https://bugs.webkit.org/show_bug.cgi?id=109909).

+public:
+    ScopedStyleResolution(StyleResolverState*, Document*, Element*, RenderStyle* parentStyle = 0, RenderRegion* regionForStyling = 0);
+    ~ScopedStyleResolution();
+private:
+    StyleResolverState* m_state;
+};
+
 class StyleResolverState {
 WTF_MAKE_NONCOPYABLE(StyleResolverState);
 public:
@@ -94,9 +103,6 @@ public:
     , m_styleMap(*this, m_elementStyleResources)
     { }
 
-    void initForStyleResolve(Document*, Element*, RenderStyle* parentStyle = 0, RenderRegion* regionForStyling = 0);
-    void clear();
-
     // These are all just pass-through methods to ElementResolveContext.
     Document* document() const { return m_elementContext.document(); }
     Element* element() const { return m_elementContext.element(); }
@@ -176,6 +182,11 @@ public:
     bool useSVGZoomRules() const { return element() && element()->isSVGElement(); }
 
 private:
+    friend class ScopedStyleResolution;
+
+    void initForStyleResolve(Document*, Element*, RenderStyle* parentStyle = 0, RenderRegion* regionForStyling = 0);
+    void clear();
+
     void initElement(Element*);
 
     ElementResolveContext m_elementContext;