Let StyleResolver figure out differences between UA style and resolved style.

Source/core/layout/style/AuthorStyleInfo.h

Index: Source/core/layout/style/AuthorStyleInfo.h
diff --git a/Source/core/layout/style/AuthorStyleInfo.h b/Source/core/layout/style/AuthorStyleInfo.h
new file mode 100644
index 0000000000000000000000000000000000000000..290892ac44917fb556ab653786f8b17945ade170
--- /dev/null
+++ b/Source/core/layout/style/AuthorStyleInfo.h
@@ -0,0 +1,32 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef AuthorStyleInfo_h
+#define AuthorStyleInfo_h
+
+namespace blink {
+
+// This class knows whether the author specified a background and/or border on
+// some element. Some control elements use this information to figure out if the
+// element is sufficiently styled by the author to disable the native look.
+class AuthorStyleInfo {
+public:
+    AuthorStyleInfo() : AuthorStyleInfo(false, false) { }
+    AuthorStyleInfo(bool specifiesBackground, bool specifiesBorder)
+        : m_specifiesBackground(specifiesBackground)
+        , m_specifiesBorder(specifiesBorder)
+    {
+    }
+
+    bool specifiesBackground() const { return m_specifiesBackground; };
+    bool specifiesBorder() const { return m_specifiesBorder; };
+
+private:
+    bool m_specifiesBackground;
+    bool m_specifiesBorder;
+};
+
+} // namespace blink
+
+#endif // AuthorStyleInfo_h