Support colors w/ alpha in SVG 'stop' elements and 'feFlood'

Source/platform/graphics/Color.cpp

Index: Source/platform/graphics/Color.cpp
diff --git a/Source/platform/graphics/Color.cpp b/Source/platform/graphics/Color.cpp
index 97b568a1a9eaf868f60b175dd7ebc29622cb72e0..2399047805b208410a2da297bce2bc33e1667922 100644
--- a/Source/platform/graphics/Color.cpp
+++ b/Source/platform/graphics/Color.cpp
@@ -312,6 +312,11 @@ Color Color::dark() const
                  alpha());
 }
 
+Color Color::modulate(float factor) const
+{
+    return colorWithOverrideAlpha(rgb(), (alpha() / 255.f) * factor);
+}
+
 static int blendComponent(int c, int a)
 {
     // We use white.