Add unit test for GlyphPageTreeNode.

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 a81ac2a4c9fb00a83657899c71264233033fbf4b..5c045b69d465b193bde315465aa03866545134bd 100644
--- a/Source/platform/fonts/GlyphPageTreeNode.cpp
+++ b/Source/platform/fonts/GlyphPageTreeNode.cpp
@@ -124,7 +124,7 @@ static bool fill(GlyphPage* pageToFill, unsigned offset, unsigned length, UChar*
     if (fontData->isSVGFont())
         return fontData->customFontData()->fillSVGGlyphPage(pageToFill, offset, length, buffer, bufferLength, fontData);
 #endif
-    bool hasGlyphs = pageToFill->fill(offset, length, buffer, bufferLength, fontData);
+    bool hasGlyphs = fontData->fillGlyphPage(pageToFill, offset, length, buffer, bufferLength);
 #if ENABLE(OPENTYPE_VERTICAL)
     if (hasGlyphs && fontData->verticalData())
         fontData->verticalData()->substituteWithVerticalGlyphs(fontData, pageToFill, offset, length);