Make RenderObject::style() return a const object

Source/core/dom/NodeLayoutStyle.h

Index: Source/core/dom/NodeLayoutStyle.h
diff --git a/Source/core/dom/NodeLayoutStyle.h b/Source/core/dom/NodeLayoutStyle.h
index e5094a9ddf5212fa3469515f7abb9b854043e99d..feaa0d5caec5ca5417b104e16bd7f8a87c881eb3 100644
--- a/Source/core/dom/NodeLayoutStyle.h
+++ b/Source/core/dom/NodeLayoutStyle.h
@@ -33,10 +33,10 @@
 
 namespace blink {
 
-inline LayoutStyle* Node::layoutStyle() const
+inline LayoutStyle* Node::mutableLayoutStyle() const
 {
     if (LayoutObject* renderer = this->renderer())
-        return renderer->style();
+        return renderer->mutableStyle();
     // <option> and <optgroup> can be styled even if they don't get renderers,
     // so they store their style internally and return it through nonRendererStyle().
     // We check here explicitly to avoid the virtual call in the common case.
@@ -45,7 +45,12 @@ inline LayoutStyle* Node::layoutStyle() const
     return 0;
 }
 
-inline LayoutStyle* Node::parentLayoutStyle() const
+inline const LayoutStyle* Node::layoutStyle() const
+{
+    return mutableLayoutStyle();
+}
+
+inline const LayoutStyle* Node::parentLayoutStyle() const
 {
     ContainerNode* parent = NodeRenderingTraversal::parent(*this);
     return parent ? parent->layoutStyle() : 0;