Add @override annotation to known overriden methods

sky/sdk/lib/painting/text_style.dart

Index: sky/sdk/lib/painting/text_style.dart
diff --git a/sky/sdk/lib/painting/text_style.dart b/sky/sdk/lib/painting/text_style.dart
index 1ebc558fa7ca2697632c55455662dc443e5c2a27..dfecfd8bce902c6925352d3622e3753669f38be6 100644
--- a/sky/sdk/lib/painting/text_style.dart
+++ b/sky/sdk/lib/painting/text_style.dart
@@ -152,20 +152,22 @@ class TextStyle {
     }
   }
 
+  @override
   bool operator ==(other) {
     if (identical(this, other))
       return true;
     return other is TextStyle &&
       color == other.color &&
-      fontFamily == other.fontFamily && 
+      fontFamily == other.fontFamily &&
       fontSize == other.fontSize &&
       fontWeight == other.fontWeight &&
-      textAlign == other.textAlign && 
+      textAlign == other.textAlign &&
       decoration == other.decoration &&
       decorationColor == other.decorationColor &&
       decorationStyle == other.decorationStyle;
   }
 
+  @override
   int get hashCode {
     // Use Quiver: https://github.com/domokit/mojo/issues/236
     int value = 373;
@@ -180,6 +182,7 @@ class TextStyle {
     return value;
   }
 
+  @override
   String toString([String prefix = '']) {
     List<String> result = [];
     if (color != null)