Have Blink be told of scrollbar changes rather than paying attention itself (Blink side part 2).

Source/core/platform/ScrollbarThemeMacCommon.mm

 /*
  * Copyright (C) 2008, 2011 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 52 matching lines @@
 typedef HashSet<ScrollbarThemeClient*> ScrollbarSet;
 
 static ScrollbarSet& scrollbarSet()
 {
     DEFINE_STATIC_LOCAL(ScrollbarSet, set, ());
     return set;
 }
 
 }
 
-@interface WebScrollbarPrefsObserver : NSObject
-{
-}
-
-+ (void)registerAsObserver;
-+ (void)appearancePrefsChanged:(NSNotification*)theNotification;
-+ (void)behaviorPrefsChanged:(NSNotification*)theNotification;
-
-@end
-
-@implementation WebScrollbarPrefsObserver
-
-+ (void)appearancePrefsChanged:(NSNotification*)unusedNotification
-{
-    UNUSED_PARAM(unusedNotification);
-
-    ScrollbarTheme* theme = ScrollbarTheme::theme();
-    if (theme->isMockTheme())
-        return;
-
-    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
-    [defaults synchronize];
-    static_cast<ScrollbarThemeMacCommon*>(ScrollbarTheme::theme())->preferencesChanged(
-        [defaults floatForKey:@"NSScrollerButtonDelay"], [defaults floatForKey:@"NSScrollerButtonPeriod"],
-        [defaults boolForKey:@"AppleScrollerPagingBehavior"], true);
-}
-
-+ (void)behaviorPrefsChanged:(NSNotification*)unusedNotification
-{
-    UNUSED_PARAM(unusedNotification);
-
-    ScrollbarTheme* theme = ScrollbarTheme::theme();
-    if (theme->isMockTheme())
-        return;
-
-    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
-    [defaults synchronize];
-    static_cast<ScrollbarThemeMacCommon*>(ScrollbarTheme::theme())->preferencesChanged(
-        [defaults floatForKey:@"NSScrollerButtonDelay"], [defaults floatForKey:@"NSScrollerButtonPeriod"],
-        [defaults boolForKey:@"AppleScrollerPagingBehavior"], false);
-}
-
-+ (void)registerAsObserver
-{
-    [[NSDistributedNotificationCenter defaultCenter] addObserver:self selector:@selector(appearancePrefsChanged:) name:@"AppleAquaScrollBarVariantChanged" object:nil suspensionBehavior:NSNotificationSuspensionBehaviorDeliverImmediately];
-    [[NSDistributedNotificationCenter defaultCenter] addObserver:self selector:@selector(behaviorPrefsChanged:) name:@"AppleNoRedisplayAppearancePreferenceChanged" object:nil suspensionBehavior:NSNotificationSuspensionBehaviorCoalesce];
-}
-
-@end
-
 namespace WebCore {
 
 static float gInitialButtonDelay = 0.5f;
 static float gAutoscrollButtonDelay = 0.05f;
 static bool gJumpOnTrackClick = false;
 
 ScrollbarTheme* ScrollbarTheme::nativeTheme()
 {
     static ScrollbarThemeMacCommon* theme = NULL;
     if (theme)
         return theme;
     if (isScrollbarOverlayAPIAvailable()) {
         DEFINE_STATIC_LOCAL(ScrollbarThemeMacOverlayAPI, overlayTheme, ());
         theme = &overlayTheme;
     } else {
         DEFINE_STATIC_LOCAL(ScrollbarThemeMacNonOverlayAPI, nonOverlayTheme, ());
         theme = &nonOverlayTheme;
     }
-    theme->Initialize();
     return theme;
 }
 
 void ScrollbarThemeMacCommon::registerScrollbar(ScrollbarThemeClient* scrollbar)
 {
     scrollbarSet().add(scrollbar);
 }
 
 void ScrollbarThemeMacCommon::unregisterScrollbar(ScrollbarThemeClient* scrollbar)
 {
@@ skipping 180 matching lines @@
     if (!tickmarks.size())
         return;
 
     // Inset a bit.
     IntRect tickmarkTrackRect = rect;
     tickmarkTrackRect.setX(tickmarkTrackRect.x() + 1);
     tickmarkTrackRect.setWidth(tickmarkTrackRect.width() - 2);
     paintGivenTickmarks(context, scrollbar, tickmarkTrackRect, tickmarks);
 }
 
-void ScrollbarThemeMacCommon::Initialize()
-{
-    [WebScrollbarPrefsObserver registerAsObserver];
-    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
-    [defaults synchronize];
-    preferencesChanged(
-        [defaults floatForKey:@"NSScrollerButtonDelay"], [defaults floatForKey:@"NSScrollerButtonPeriod"],
-        [defaults boolForKey:@"AppleScrollerPagingBehavior"], false);
-}
-
 ScrollbarThemeMacCommon::~ScrollbarThemeMacCommon()
 {
 }
 
 void ScrollbarThemeMacCommon::preferencesChanged(float initialButtonDelay, float autoscrollButtonDelay, bool jumpOnTrackClick, bool redraw)
 {
     updateButtonPlacement();
     gInitialButtonDelay = initialButtonDelay;
     gAutoscrollButtonDelay = autoscrollButtonDelay;
     gJumpOnTrackClick = jumpOnTrackClick;
@@ skipping 42 matching lines @@
         case ForwardButtonEndPart:
             return kThemeBottomOutsideArrowPressed;
         case ThumbPart:
             return kThemeThumbPressed;
         default:
             return 0;
     }
 }
 
 } // namespace WebCore