Re-enable Yaml tests on dart2js and dartc.

utils/pub/yaml/parser.dart

Index: utils/pub/yaml/parser.dart
diff --git a/utils/pub/yaml/parser.dart b/utils/pub/yaml/parser.dart
index f19ab7865a28699edf513a5be0edc4eba0cfcdf8..1753bd6647f148fad2a7e4b1db80c38b62111093 100644
--- a/utils/pub/yaml/parser.dart
+++ b/utils/pub/yaml/parser.dart
@@ -248,6 +248,7 @@ class _Parser {
       if (!truth(el)) return out;
       out.add(el);
     }
+    return null; // unreachable

[Bob Nystrom, 2012/05/24 22:36:50]

"Unreachable."

   }
 
   /**
@@ -266,6 +267,7 @@ class _Parser {
       oldPos = pos;
       out.add(el);
     }
+    return null; // unreachable
   }
 
   /**
@@ -1838,6 +1840,7 @@ class _Parser {
     var doc = l_explicitDocument();
     if (doc != null) return doc;
     parseFailed();
+    return null; // unreachable
   }
 
   // 210