Make RenderObject::style() return a const object

Source/core/layout/LayoutTheme.cpp

Index: Source/core/layout/LayoutTheme.cpp
diff --git a/Source/core/layout/LayoutTheme.cpp b/Source/core/layout/LayoutTheme.cpp
index 5705d4167a046c771ed54632c8fb85e8bd0c811e..9943c9e990a4e97c59e7698b7990e55aea93242e 100644
--- a/Source/core/layout/LayoutTheme.cpp
+++ b/Source/core/layout/LayoutTheme.cpp
@@ -839,7 +839,7 @@ void LayoutTheme::paintSliderTicks(RenderObject* o, const PaintInfo& paintInfo,
     IntSize thumbSize;
     RenderObject* thumbRenderer = input->userAgentShadowRoot()->getElementById(ShadowElementNames::sliderThumb())->renderer();
     if (thumbRenderer) {
-        RenderStyle* thumbStyle = thumbRenderer->style();
+        const RenderStyle* thumbStyle = thumbRenderer->style();
         int thumbWidth = thumbStyle->width().intValue();
         int thumbHeight = thumbStyle->height().intValue();
         thumbSize.setWidth(isHorizontal ? thumbWidth : thumbHeight);
@@ -1139,7 +1139,7 @@ bool LayoutTheme::supportsCalendarPicker(const AtomicString& type) const
 }
 #endif
 
-bool LayoutTheme::shouldUseFallbackTheme(RenderStyle*) const
+bool LayoutTheme::shouldUseFallbackTheme(const RenderStyle*) const
 {
     return false;
 }