Make RenderObject::style() return a const object

Source/web/tests/WebFrameTest.cpp

Index: Source/web/tests/WebFrameTest.cpp
diff --git a/Source/web/tests/WebFrameTest.cpp b/Source/web/tests/WebFrameTest.cpp
index a9b2f35a315b3cf45519b7fe17902826e62a8e2d..5de7a0744f53e3328026de0c6b04cf36cb8757eb 100644
--- a/Source/web/tests/WebFrameTest.cpp
+++ b/Source/web/tests/WebFrameTest.cpp
@@ -704,10 +704,10 @@ static bool setTextAutosizingMultiplier(Document* document, float multiplier)
 {
     bool multiplierSet = false;
     for (LayoutObject* renderer = document->renderView(); renderer; renderer = renderer->nextInPreOrder()) {
-        if (renderer->style()) {
-            renderer->style()->setTextAutosizingMultiplier(multiplier);
+        if (LayoutStyle* style = renderer->mutableStyle()) {
+            style->setTextAutosizingMultiplier(multiplier);
 
-            EXPECT_EQ(multiplier, renderer->style()->textAutosizingMultiplier());
+            EXPECT_EQ(multiplier, style->textAutosizingMultiplier());
             multiplierSet = true;
         }
     }