Cache results from respondsToSelector.

Source/core/platform/mac/NSScrollerImpDetails.mm

 /*
  * Copyright (C) 2011 Apple Inc. All Rights Reserved.
  * Copyright (C) 2011 Google 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
@@ skipping 30 matching lines @@
         Class scrollerImpPairClass = NSClassFromString(@"NSScrollerImpPair");
         apiAvailable = [scrollerImpClass respondsToSelector:@selector(scrollerImpWithStyle:controlSize:horizontal:replacingScrollerImp:)]
                        && [scrollerImpPairClass instancesRespondToSelector:@selector(scrollerStyle)];
     }
     return apiAvailable;
 }
 
 NSScrollerStyle recommendedScrollerStyle() {
     if (RuntimeEnabledFeatures::overlayScrollbarsEnabled())
         return NSScrollerStyleOverlay;
-    if ([NSScroller respondsToSelector:@selector(preferredScrollerStyle)])

[Nico, 2013/10/11 19:48:48]

If this is called from a single thread, just 

static bool respondsToPreferredScrollerStyle = [NSScroller
respondsToSelector:@selector(preferredScrollerStyle)];  // static for speed

would be enough and a tad shorter.

+    bool respondsToSelectorPreferredScrollerStyle;
+    bool shouldInitialize = true;

[Nico, 2013/10/11 19:48:48]

…wait, how does this version work? Isn't this still called every frame? Did you
check in a profiler that the hotspot actually goes away?

+    if (shouldInitialize) {
+        shouldInitialize = false;
+        respondsToSelectorPreferredScrollerStyle = [NSScroller respondsToSelector:@selector(preferredScrollerStyle)];
+    }
+    if (respondsToSelectorPreferredScrollerStyle)
         return [NSScroller preferredScrollerStyle];
     return NSScrollerStyleLegacy;
 }
 
 }