Add API to send NSUserDefault values over IPC, while preserving current behavior

public/web/mac/WebScrollbarTheme.h

Index: public/web/mac/WebScrollbarTheme.h
diff --git a/public/web/mac/WebScrollbarTheme.h b/public/web/mac/WebScrollbarTheme.h
index 50b543b54d8a4a49fa3f7925a75747709a5b02ee..4ba409d6c4f709b23088c4287a2feb9bfc88e3fd 100644
--- a/public/web/mac/WebScrollbarTheme.h
+++ b/public/web/mac/WebScrollbarTheme.h
@@ -33,6 +33,8 @@
 
 #include "public/platform/WebCommon.h"
 
+#include <string>
+
 namespace blink {
 
 // This enum must match NSScrollerStyle in the 10.7 SDK.
@@ -48,9 +50,15 @@ public:
     // |autoscrollButtonDelay| is the current value of NSScrollerButtonPeriod from NSUserDefaults.
     // |preferredScrollerStyle| is the current value of +[NSScroller preferredScrollerStyle].
     // |redraw| is true if the update requires a redraw to include the change.
+    // |scrollAnimationEnabled| is the current value of NSScrollAnimationEnabled or AppleScrollAnimationEnabled from NSUserDefaults.
+    // |buttonPlacement| is the current value of AppleScrollBarVariant
     BLINK_EXPORT static void updateScrollbars(
         float initialButtonDelay, float autoscrollButtonDelay,
         ScrollerStyle preferredScrollerStyle, bool redraw);
+    BLINK_EXPORT static void updateScrollbarsWithNSDefaults(
+        float initialButtonDelay, float autoscrollButtonDelay,
+        ScrollerStyle preferredScrollerStyle, bool redraw,
+        bool scrollAnimationEnabled, const std::string& buttonPlacement);
 };
 
 } // namespace blink