Introduce DEFINE_FONT_DATA_TYPE_CASTS, and use it

Source/platform/fonts/FontFallbackList.cpp

Index: Source/platform/fonts/FontFallbackList.cpp
diff --git a/Source/platform/fonts/FontFallbackList.cpp b/Source/platform/fonts/FontFallbackList.cpp
index 05d9fd3f5071e45bbf21a8056904273046570225..fbf4debda102f4ac4d70c4b06107af4a0d74c2ba 100644
--- a/Source/platform/fonts/FontFallbackList.cpp
+++ b/Source/platform/fonts/FontFallbackList.cpp
@@ -71,7 +71,7 @@ void FontFallbackList::releaseFontData()
     for (unsigned i = 0; i < numFonts; ++i) {
         if (!m_fontList[i]->isCustomFont()) {
             ASSERT(!m_fontList[i]->isSegmented());
-            FontCache::fontCache()->releaseFontData(static_cast<const SimpleFontData*>(m_fontList[i].get()));
+            FontCache::fontCache()->releaseFontData(toSimpleFontData(m_fontList[i]));
         }
     }
 }
@@ -95,7 +95,7 @@ void FontFallbackList::determinePitch(const FontDescription& fontDescription) co
             }
             simpleFontData = segmentedFontData->rangeAt(0).fontData().get();
         } else {
-            simpleFontData = static_cast<const SimpleFontData*>(fontData);
+            simpleFontData = toSimpleFontData(fontData);
         }
         if (!fontData->isLoadingFallback()) {
             m_pitch = simpleFontData->pitch();