Merge pull request #1797 from Hixie/toString

toString for Tween and ThemeData

packages/flutter/lib/src/animation/tween.dart

@@ -75,6 +75,8 @@ class Tween<T extends dynamic> extends Animatable<T> {
       return end;
     return lerp(t);
   }
+
+  String toString() => '$runtimeType($begin \u2192 $end)';
 }
 
 /// An interpolation between two colors.

packages/flutter/lib/src/material/theme_data.dart

@@ -285,5 +285,5 @@ class ThemeData {
     );
   }
 
-  String toString() => '$primaryColor $brightness etc...';
+  String toString() => '$runtimeType($brightness $primaryColor etc...)';
 }