Make RenderObject::style() return a const object

Source/core/rendering/RenderBoxModelObject.cpp

Index: Source/core/rendering/RenderBoxModelObject.cpp
diff --git a/Source/core/rendering/RenderBoxModelObject.cpp b/Source/core/rendering/RenderBoxModelObject.cpp
index 86c16367ea4b217751e49bf6b0564437d1c4d482..5c5b0dd01d0b6be88eb86c520e37a26769ddf91b 100644
--- a/Source/core/rendering/RenderBoxModelObject.cpp
+++ b/Source/core/rendering/RenderBoxModelObject.cpp
@@ -113,7 +113,7 @@ void RenderBoxModelObject::willBeDestroyed()
 
 bool RenderBoxModelObject::calculateHasBoxDecorations() const
 {
-    RenderStyle* styleToUse = style();
+    const RenderStyle* styleToUse = style();
     ASSERT(styleToUse);
     return hasBackground() || styleToUse->hasBorder() || styleToUse->hasAppearance() || styleToUse->boxShadow();
 }
@@ -122,7 +122,7 @@ void RenderBoxModelObject::updateFromStyle()
 {
     RenderLayerModelObject::updateFromStyle();
 
-    RenderStyle* styleToUse = style();
+    const RenderStyle* styleToUse = style();
     setHasBoxDecorationBackground(calculateHasBoxDecorations());
     setInline(styleToUse->isDisplayInlineType());
     setPositionState(styleToUse->position());
@@ -500,7 +500,7 @@ LayoutRect RenderBoxModelObject::localCaretRectForEmptyElement(LayoutUnit width,
     // However, as soon as some content is entered, the line boxes will be
     // constructed and this kludge is not called any more. So only the caret size
     // of an empty :first-line'd block is wrong. I think we can live with that.
-    RenderStyle* currentStyle = firstLineStyle();
+    const RenderStyle* currentStyle = firstLineStyle();
 
     enum CaretAlignment { alignLeft, alignRight, alignCenter };