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

Source/platform/graphics/Color.h

Index: Source/platform/graphics/Color.h
diff --git a/Source/platform/graphics/Color.h b/Source/platform/graphics/Color.h
index 9664906a8f7840954ce28a951d56656c4d053db0..f58e8cb59c50adcf41c5c33c5ced546e58b33a5b 100644
--- a/Source/platform/graphics/Color.h
+++ b/Source/platform/graphics/Color.h
@@ -113,6 +113,8 @@ public:
     Color light() const;
     Color dark() const;
 
+    Color modulate(float factor) const;
+
     // This is an implementation of Porter-Duff's "source-over" equation
     Color blend(const Color&) const;
     Color blendWithWhite() const;