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

Source/core/rendering/style/UAStyleChange.h

Index: Source/core/rendering/style/UAStyleChange.h
diff --git a/Source/core/rendering/style/UAStyleChange.h b/Source/core/rendering/style/UAStyleChange.h
new file mode 100644
index 0000000000000000000000000000000000000000..d3461ae79ee5ed09a88864c255e0e93dd430de83
--- /dev/null
+++ b/Source/core/rendering/style/UAStyleChange.h
@@ -0,0 +1,26 @@
+// 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 UAStyleChange_h
+#define UAStyleChange_h
+
+namespace blink {
+
+class UAStyleChange {
+public:
+    UAStyleChange(bool hasAppearance)
+        : hasAppearance(hasAppearance)
+        , backgroundChanged(false)
+        , borderChanged(false)
+    {
+    }
+
+    bool hasAppearance;

[Timothy Loh, 2015/02/06 00:20:29]

m_ for members

+    bool backgroundChanged;
+    bool borderChanged;
+};
+
+} // namespace blink
+
+#endif // UAStyleChange_h