Introduce DEFINE_FONT_DATA_TYPE_CASTS, and use it

Source/platform/fonts/GlyphPageTreeNode.cpp

Index: Source/platform/fonts/GlyphPageTreeNode.cpp
diff --git a/Source/platform/fonts/GlyphPageTreeNode.cpp b/Source/platform/fonts/GlyphPageTreeNode.cpp
index 3f0537f32b5a5fcb870a54c0ee483117b59d30eb..baa42fc2952da4daf0ffb852d09aadb47a1728c1 100644
--- a/Source/platform/fonts/GlyphPageTreeNode.cpp
+++ b/Source/platform/fonts/GlyphPageTreeNode.cpp
@@ -207,13 +207,13 @@ void GlyphPageTreeNode::initializePage(const FontData* fontData, unsigned pageNu
             // for only 128 out of 256 characters.
             bool haveGlyphs;
             if (!fontData->isSegmented()) {
-                m_page = GlyphPage::createForSingleFontData(this, static_cast<const SimpleFontData*>(fontData));
-                haveGlyphs = fill(m_page.get(), 0, GlyphPage::size, buffer, bufferLength, static_cast<const SimpleFontData*>(fontData));
+                m_page = GlyphPage::createForSingleFontData(this, toSimpleFontData(fontData));
+                haveGlyphs = fill(m_page.get(), 0, GlyphPage::size, buffer, bufferLength, toSimpleFontData(fontData));
             } else {
                 m_page = GlyphPage::createForMixedFontData(this);
                 haveGlyphs = false;
 
-                const SegmentedFontData* segmentedFontData = static_cast<const SegmentedFontData*>(fontData);
+                const SegmentedFontData* segmentedFontData = toSegmentedFontData(fontData);
                 for (int i = segmentedFontData->numRanges() - 1; i >= 0; i--) {
                     const FontDataRange& range = segmentedFontData->rangeAt(i);
                     // all this casting is to ensure all the parameters to min and max have the same type,