Improve RAII of StyleResolverState.

Source/core/css/resolver/FontBuilder.cpp

Index: Source/core/css/resolver/FontBuilder.cpp
diff --git a/Source/core/css/resolver/FontBuilder.cpp b/Source/core/css/resolver/FontBuilder.cpp
index a0cc60f30b974333e9b440d58ec892fdcb5ed2ae..28c8331fd6445d3be1426913c759873c133c1b57 100644
--- a/Source/core/css/resolver/FontBuilder.cpp
+++ b/Source/core/css/resolver/FontBuilder.cpp
@@ -60,11 +60,12 @@ private:
     FontDescription m_fontDescription;
 };
 
-FontBuilder::FontBuilder(const Document& document)
+FontBuilder::FontBuilder(const Document& document, RenderStyle* style)
     : m_document(document)
-    , m_style(nullptr)
+    , m_style(style)
     , m_fontDirty(false)
 {
+    ASSERT(style);
     ASSERT(document.frame());
 }