Do not call CGFontSetShouldUseMulticache. Apple says to not.

Source/core/platform/graphics/mac/FontCacheMac.mm

 /*
  * Copyright (C) 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Nicholas Shanks <webkit@nickshanks.com>
  *
  * 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. 
@@ skipping 21 matching lines @@
 
 #import <AppKit/AppKit.h>
 #import "core/platform/graphics/Font.h"
 #import "core/platform/graphics/FontPlatformData.h"
 #import "core/platform/graphics/SimpleFontData.h"
 #import "core/platform/mac/WebFontCache.h"
 #import <wtf/MainThread.h>
 #import <wtf/StdLibExtras.h>
 
 // Forward declare Mac SPIs.
-// Request for public API: rdar://13787490
-extern "C" {
-void CGFontSetShouldUseMulticache(bool enable);
-}
-
 // Request for public API: rdar://13803570
 @interface NSFont (WebKitSPI)
 + (NSFont*)findFontLike:(NSFont*)font forString:(NSString*)string withRange:(NSRange)range inLanguage:(id)useNil;
 + (NSFont*)findFontLike:(NSFont*)font forCharacter:(UniChar)uc inLanguage:(id)useNil;
 @end
 
 namespace WebCore {
 
 // The "void*" parameter makes the function match the prototype for callbacks from callOnMainThread.
 static void invalidateFontCache(void*)
 {
     if (!isMainThread()) {
         callOnMainThread(&invalidateFontCache, 0);
         return;
     }
     fontCache()->invalidate();
 }
 
 static void fontCacheRegisteredFontsChangedNotificationCallback(CFNotificationCenterRef, void* observer, CFStringRef name, const void *, CFDictionaryRef)
 {
     ASSERT_UNUSED(observer, observer == fontCache());
     ASSERT_UNUSED(name, CFEqual(name, kCTFontManagerRegisteredFontsChangedNotification));
     invalidateFontCache(0);
 }
 
 void FontCache::platformInit()
 {
-    // Note: This may break on future OS releases, per https://bugs.webkit.org/show_bug.cgi?id=102405#c8.
-    CGFontSetShouldUseMulticache(true);
     CFNotificationCenterAddObserver(CFNotificationCenterGetLocalCenter(), this, fontCacheRegisteredFontsChangedNotificationCallback, kCTFontManagerRegisteredFontsChangedNotification, 0, CFNotificationSuspensionBehaviorDeliverImmediately);
 }
 
 static int toAppKitFontWeight(FontWeight fontWeight)
 {
     static int appKitFontWeights[] = {
         2,  // FontWeight100
         3,  // FontWeight200
         4,  // FontWeight300
         5,  // FontWeight400
@@ skipping 148 matching lines @@
 
     // FontPlatformData::font() can be null for the case of Chromium out-of-process font loading.
     // In that case, we don't want to use the platformData.
     OwnPtr<FontPlatformData> platformData = adoptPtr(new FontPlatformData(platformFont, size, fontDescription.usePrinterFont(), syntheticBold, syntheticOblique, fontDescription.orientation(), fontDescription.widthVariant()));
     if (!platformData->font())
         return 0;
     return platformData.leakPtr();
 }
 
 } // namespace WebCore