Introduce DEFINE_FONT_DATA_TYPE_CASTS, and use it

Source/platform/fonts/mac/SimpleFontDataMac.mm

Index: Source/platform/fonts/mac/SimpleFontDataMac.mm
diff --git a/Source/platform/fonts/mac/SimpleFontDataMac.mm b/Source/platform/fonts/mac/SimpleFontDataMac.mm
index 0f01679331265dd2a45f5d9916758c544989a1d5..69b1801e49088d7094a7cb00c922df1dc2f7ac51 100644
--- a/Source/platform/fonts/mac/SimpleFontDataMac.mm
+++ b/Source/platform/fonts/mac/SimpleFontDataMac.mm
@@ -124,7 +124,7 @@ const SimpleFontData* SimpleFontData::getCompositeFontReferenceFontData(NSFont *
         if (!m_derivedFontData->compositeFontReferences)
             m_derivedFontData->compositeFontReferences.adoptCF(CFDictionaryCreateMutable(kCFAllocatorDefault, 1, &kCFTypeDictionaryKeyCallBacks, NULL));
         else {
-            const SimpleFontData* found = static_cast<const SimpleFontData*>(CFDictionaryGetValue(m_derivedFontData->compositeFontReferences.get(), static_cast<const void *>(key)));
+            const SimpleFontData* found = toSimpleFontData(CFDictionaryGetValue(m_derivedFontData->compositeFontReferences.get(), static_cast<const void *>(key)));
             if (found)
                 return found;
         }