Remove platform dependency upon page/Settings class which is a layering violation.

Source/core/platform/ScrollbarTheme.h

Index: Source/core/platform/ScrollbarTheme.h
diff --git a/Source/core/platform/ScrollbarTheme.h b/Source/core/platform/ScrollbarTheme.h
index 7065c2ee27522c38e9f4df63e19b9c3876ef1ec3..cd84390c2a94d027f3b9de2cebe5055f35944878 100644
--- a/Source/core/platform/ScrollbarTheme.h
+++ b/Source/core/platform/ScrollbarTheme.h
@@ -138,8 +138,12 @@ public:
 
     static ScrollbarTheme* theme();
 
+    static void setMockScrollbarsEnabled(bool flag);
+    static bool mockScrollbarsEnabled();
+
 private:
     static ScrollbarTheme* nativeTheme(); // Must be implemented to return the correct theme subclass.
+    static bool gMockScrollbarsEnabled;
 };
 
 }