Only FontCache should know about system font substitution

Source/platform/fonts/FontCache.cpp

 /*
  * Copyright (C) 2006, 2008 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 152 matching lines @@
     if (shouldRetain == DoNotRetain)
         ASSERT(m_purgePreventCount);
 #endif
 
     return gFontDataCache->get(platformData, shouldRetain);
 }
 
 bool FontCache::isPlatformFontAvailable(const FontDescription& fontDescription, const AtomicString& family)
 {
     bool checkingAlternateName = true;
-    return getFontPlatformData(fontDescription, family, checkingAlternateName);
+    return getFontPlatformData(fontDescription, adjustFamilyNameToAvoidUnsupportedFonts(family), checkingAlternateName);
 }
 
 SimpleFontData* FontCache::getNonRetainedLastResortFallbackFont(const FontDescription& fontDescription)
 {
     return getLastResortFallbackFont(fontDescription, DoNotRetain).leakRef();
 }
 
 void FontCache::releaseFontData(const SimpleFontData* fontData)
 {
     ASSERT(gFontDataCache);
@@ skipping 111 matching lines @@
         clients.append(*it);
 
     ASSERT(numClients == clients.size());
     for (size_t i = 0; i < numClients; ++i)
         clients[i]->fontCacheInvalidated();
 
     purge(ForcePurge);
 }
 
 } // namespace WebCore