Fix virtual/override/final usage in Source/platform/.

Source/platform/graphics/filters/SourceAlpha.h

Index: Source/platform/graphics/filters/SourceAlpha.h
diff --git a/Source/platform/graphics/filters/SourceAlpha.h b/Source/platform/graphics/filters/SourceAlpha.h
index 1cb4aadd9342435d1e0c3eb396e353916e35811e..b91feb181f237ffe351f5447aee6aeaa914624b9 100644
--- a/Source/platform/graphics/filters/SourceAlpha.h
+++ b/Source/platform/graphics/filters/SourceAlpha.h
@@ -31,12 +31,12 @@ public:
 
     static const AtomicString& effectName();
 
-    virtual FloatRect determineAbsolutePaintRect(const FloatRect& requestedRect) override;
+    FloatRect determineAbsolutePaintRect(const FloatRect& requestedRect) override;
 
-    virtual FilterEffectType filterEffectType() const override { return FilterEffectTypeSourceInput; }
+    FilterEffectType filterEffectType() const override { return FilterEffectTypeSourceInput; }
 
-    virtual TextStream& externalRepresentation(TextStream&, int indention) const override;
-    virtual PassRefPtr<SkImageFilter> createImageFilter(SkiaImageFilterBuilder*) override;
+    TextStream& externalRepresentation(TextStream&, int indention) const override;
+    PassRefPtr<SkImageFilter> createImageFilter(SkiaImageFilterBuilder*) override;
 
 private:
     explicit SourceAlpha(FilterEffect*);