Fix up constructor naming style for MaskFilter and ColorFilter.

sky/engine/core/painting/ColorFilter.dart

Index: sky/engine/core/painting/ColorFilter.dart
diff --git a/sky/engine/core/painting/ColorFilter.dart b/sky/engine/core/painting/ColorFilter.dart
index f7e261b18a5a7209434a0a677395fe56a20efedf..a3b61136eebb94be4efafea3ca2d91b65fc341b4 100644
--- a/sky/engine/core/painting/ColorFilter.dart
+++ b/sky/engine/core/painting/ColorFilter.dart
@@ -8,6 +8,6 @@ part of dart.sky;
 class ColorFilter extends _ColorFilter {
   // This is the only ColorFilter type we need, but use a named constructor so
   // we can add more in the future.
-  ColorFilter.Mode(Color color, TransferMode transferMode)
+  ColorFilter.mode(Color color, TransferMode transferMode)
       : super(color, transferMode) {}
 }