Revert of Revert of Move preferred scrollbar style preference change listening from renderer to browser, 3 of 3.

Source/platform/scroll/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
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "config.h"
+#include "RuntimeEnabledFeatures.h"
 #include "platform/scroll/ScrollbarThemeMacCommon.h"
 
 #include <Carbon/Carbon.h>
 #include "platform/PlatformMouseEvent.h"
 #include "platform/graphics/Gradient.h"
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/GraphicsContextStateSaver.h"
 #include "platform/graphics/GraphicsLayer.h"
 #include "platform/graphics/ImageBuffer.h"
 #include "platform/mac/ColorMac.h"
@@ skipping 30 matching lines @@
     return set;
 }
 
 }
 
 namespace WebCore {
 
 static float gInitialButtonDelay = 0.5f;
 static float gAutoscrollButtonDelay = 0.05f;
 static bool gJumpOnTrackClick = false;
+static NSScrollerStyle gPreferredScrollerStyle = NSScrollerStyleLegacy;
 
 ScrollbarTheme* ScrollbarTheme::nativeTheme()
 {
     static ScrollbarThemeMacCommon* theme = NULL;
     if (theme)
         return theme;
-    if (isScrollbarOverlayAPIAvailable()) {
+    if (ScrollbarThemeMacCommon::isOverlayAPIAvailable()) {
         DEFINE_STATIC_LOCAL(ScrollbarThemeMacOverlayAPI, overlayTheme, ());
         theme = &overlayTheme;
     } else {
         DEFINE_STATIC_LOCAL(ScrollbarThemeMacNonOverlayAPI, nonOverlayTheme, ());
         theme = &nonOverlayTheme;
     }
     return theme;
 }
 
 void ScrollbarThemeMacCommon::registerScrollbar(ScrollbarThemeClient* scrollbar)
@@ skipping 190 matching lines @@
     IntRect tickmarkTrackRect = rect;
     tickmarkTrackRect.setX(tickmarkTrackRect.x() + 1);
     tickmarkTrackRect.setWidth(tickmarkTrackRect.width() - 2);
     paintGivenTickmarks(context, scrollbar, tickmarkTrackRect, tickmarks);
 }
 
 ScrollbarThemeMacCommon::~ScrollbarThemeMacCommon()
 {
 }
 
-void ScrollbarThemeMacCommon::preferencesChanged(float initialButtonDelay, float autoscrollButtonDelay, bool jumpOnTrackClick, bool redraw)
+void ScrollbarThemeMacCommon::preferencesChanged(float initialButtonDelay, float autoscrollButtonDelay, bool jumpOnTrackClick, NSScrollerStyle preferredScrollerStyle, bool redraw)
 {
     updateButtonPlacement();
     gInitialButtonDelay = initialButtonDelay;
     gAutoscrollButtonDelay = autoscrollButtonDelay;
     gJumpOnTrackClick = jumpOnTrackClick;
+    bool sendScrollerStyleNotification = gPreferredScrollerStyle != preferredScrollerStyle;
+    gPreferredScrollerStyle = preferredScrollerStyle;
     if (redraw && !scrollbarSet().isEmpty()) {
         ScrollbarSet::iterator end = scrollbarSet().end();
         for (ScrollbarSet::iterator it = scrollbarSet().begin(); it != end; ++it) {
             (*it)->styleChanged();
             (*it)->invalidate();
         }
     }
+    if (sendScrollerStyleNotification) {
+        [[NSNotificationCenter defaultCenter]
+            postNotificationName:@"NSPreferredScrollerStyleDidChangeNotification"
+                          object:nil
+                        userInfo:@{ @"NSScrollerStyle" : @(gPreferredScrollerStyle) }];
+    }
 }
 
 double ScrollbarThemeMacCommon::initialAutoscrollTimerDelay()
 {
     return gInitialButtonDelay;
 }
 
 double ScrollbarThemeMacCommon::autoscrollTimerDelay()
 {
     return gAutoscrollButtonDelay;
@@ skipping 24 matching lines @@
             return kThemeTopInsideArrowPressed;
         case ForwardButtonEndPart:
             return kThemeBottomOutsideArrowPressed;
         case ThumbPart:
             return kThemeThumbPressed;
         default:
             return 0;
     }
 }
 
+// static
+NSScrollerStyle ScrollbarThemeMacCommon::recommendedScrollerStyle()
+{
+    if (RuntimeEnabledFeatures::overlayScrollbarsEnabled())
+        return NSScrollerStyleOverlay;
+    return gPreferredScrollerStyle;
+}
+
+// static
+bool ScrollbarThemeMacCommon::isOverlayAPIAvailable()
+{
+    static bool apiAvailable =
+        [NSClassFromString(@"NSScrollerImp") respondsToSelector:@selector(scrollerImpWithStyle:controlSize:horizontal:replacingScrollerImp:)]
+        && [NSClassFromString(@"NSScrollerImpPair") instancesRespondToSelector:@selector(scrollerStyle)];
+    return apiAvailable;
+}
+
 } // namespace WebCore