Add unit test for GlyphPageTreeNode.

Source/platform/blink_platform.gypi

 {
   'variables': {
     'platform_files': [
       'AsyncFileSystemCallbacks.h',
       'CalculationValue.cpp',
       'CalculationValue.h',
       'CheckedInt.h',
       'Clock.cpp',
       'Clock.h',
       'ColorChooser.cpp',
@@ skipping 370 matching lines @@
       'fonts/harfbuzz/HarfBuzzShaper.h',
       'fonts/linux/FontCacheLinux.cpp',
       'fonts/linux/FontPlatformDataLinuxHarfBuzz.cpp',
       'fonts/mac/ComplexTextController.cpp',
       'fonts/mac/ComplexTextController.h',
       'fonts/mac/ComplexTextControllerCoreText.mm',
       'fonts/mac/FontCacheMac.mm',
       'fonts/mac/FontComplexTextMac.cpp',
       'fonts/mac/FontCustomPlatformDataMac.cpp',
       'fonts/mac/FontMac.cpp',
-      'fonts/mac/GlyphPageTreeNodeMac.cpp',
       'fonts/mac/MemoryActivatedFont.h',
       'fonts/mac/MemoryActivatedFont.mm',
       'fonts/mac/SimpleFontDataCoreText.cpp',
       'fonts/mac/SimpleFontDataMac.mm',
       'fonts/opentype/OpenTypeSanitizer.cpp',
       'fonts/opentype/OpenTypeSanitizer.h',
       'fonts/opentype/OpenTypeTypes.h',
       'fonts/opentype/OpenTypeUtilities.cpp',
       'fonts/opentype/OpenTypeUtilities.h',
       'fonts/opentype/OpenTypeVerticalData.cpp',
       'fonts/opentype/OpenTypeVerticalData.h',
       'fonts/skia/FontCacheSkia.cpp',
       'fonts/skia/FontCustomPlatformDataSkia.cpp',
       'fonts/skia/FontPlatformDataSkia.cpp',
-      'fonts/skia/GlyphPageTreeNodeSkia.cpp',
       'fonts/skia/SimpleFontDataSkia.cpp',
       'fonts/win/FontCacheSkiaWin.cpp',
       'fonts/win/FontFallbackWin.cpp',
       'fonts/win/FontFallbackWin.h',
       'fonts/win/FontPlatformDataWin.cpp',
       'geometry/FloatBoxExtent.h',
       'geometry/FloatPolygon.cpp',
       'geometry/FloatPolygon.h',
       'geometry/FloatPoint.cpp',
       'geometry/FloatPoint.h',
@@ skipping 467 matching lines @@
       'PurgeableVectorTest.cpp',
       'SharedBufferTest.cpp',
       'TestingPlatformSupport.cpp',
       'TestingPlatformSupport.h',
       'animation/TimingFunctionTest.cpp',
       'animation/UnitBezierTest.cpp',
       'clipboard/ClipboardUtilitiesTest.cpp',
       'fonts/FontCacheTest.cpp',
       'fonts/FontDescriptionTest.cpp',
       'fonts/FontTest.cpp',
+      'fonts/GlyphPageTreeNodeTest.cpp',
       'fonts/android/FontCacheAndroidTest.cpp',
       'geometry/FloatPolygonTest.cpp',
       'geometry/FloatRoundedRectTest.cpp',
       'geometry/RegionTest.cpp',
       'geometry/RoundedRectTest.cpp',
       'graphics/GraphicsContextTest.cpp',
       'graphics/ThreadSafeDataTransportTest.cpp',
       'graphics/filters/FilterOperationsTest.cpp',
       'graphics/filters/ImageFilterBuilderTest.cpp',
       'graphics/gpu/DrawingBufferTest.cpp',
@@ skipping 26 matching lines @@
       'graphics/ImageLayerChromiumTest.cpp',
       'graphics/OpaqueRectTrackingContentLayerDelegateTest.cpp',
       'graphics/test/MockImageDecoder.h',
       'graphics/test/MockWebGraphicsContext3D.h',
       'image-decoders/gif/GIFImageDecoderTest.cpp',
       'image-decoders/jpeg/JPEGImageDecoderTest.cpp',
       'image-decoders/webp/WEBPImageDecoderTest.cpp',
     ],
   },
 }