Have Blink be told of scrollbar changes rather than paying attention itself (Blink side).

public/web/mac/WebScrollbarTheme.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
- * Copyright (C) 2013 Intel Corporation. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
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  * notice, this list of conditions and the following disclaimer.
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  * copyright notice, this list of conditions and the following disclaimer
  * in the documentation and/or other materials provided with the
  * distribution.
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  * contributors may be used to endorse or promote products derived from
  * this software without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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  */
 
-#ifndef WebFilterKeyframe_h
-#define WebFilterKeyframe_h
+#ifndef WebScrollbarTheme_h
+#define WebScrollbarTheme_h
 
-#include "WebFilterOperations.h"
-#include "WebPrivateOwnPtr.h"
-
-#if INSIDE_BLINK
-namespace WTF { template <typename T> class PassOwnPtr; }
-#endif
+#include "public/platform/WebCommon.h"
 
 namespace WebKit {
 
-class WebFilterKeyframe {
+class WebScrollbarTheme {
 public:
-#if INSIDE_BLINK
-    BLINK_PLATFORM_EXPORT WebFilterKeyframe(double time, PassOwnPtr<WebFilterOperations>);
+#if OS(MACOSX)

[abarth-chromium, 2013/11/04 17:19:40]

Does this work in this header?  I don't think this will work when you include
this header in a Chromium file.

[Avi (use Gerrit), 2013/11/04 17:20:50]

Mmmm. Good point.

+    // Updates the scrollbar appearance and behavior.
+    // |initialButtonDelay| is the current value of NSScrollerButtonDelay from NSUserDefaults.
+    // |autoscrollButtonDelay| is the current value of NSScrollerButtonPeriod from NSUserDefaults.
+    // |jumpOnTrackClick| is the current value of AppleScrollerPagingBehavior from NSUserDefaults.
+    // |redraw| is true if the update requires a redraw to include the change.
+    BLINK_EXPORT static void updateScrollbars(
+        float initialButtonDelay, float autoscrollButtonDelay,
+        bool jumpOnTrackClick, bool redraw);
 #endif
-
-    BLINK_PLATFORM_EXPORT ~WebFilterKeyframe();
-
-    double time() const { return m_time; }
-
-    const WebFilterOperations& value() const { return *m_value.get(); }
-
-private:
-    double m_time;
-    WebPrivateOwnPtr<WebFilterOperations> m_value;
 };
 
 } // namespace WebKit
 
-#endif // WebFilterKeyframe_h
+#endif