dart2js inferrer: don't infer widened type when unreachable

pkg/compiler/lib/src/inferrer/inferrer_visitor.dart

Index: pkg/compiler/lib/src/inferrer/inferrer_visitor.dart
diff --git a/pkg/compiler/lib/src/inferrer/inferrer_visitor.dart b/pkg/compiler/lib/src/inferrer/inferrer_visitor.dart
index 65e7439aa4e42047685a2d3700f80e9bd5c27c29..8286b338d071e1463ad99b0169a95fdac7ab3c20 100644
--- a/pkg/compiler/lib/src/inferrer/inferrer_visitor.dart
+++ b/pkg/compiler/lib/src/inferrer/inferrer_visitor.dart
@@ -314,10 +314,6 @@ class ArgumentsTypes<T> extends IterableMixin<T> {
 
   bool hasNoArguments() => positional.isEmpty && named.isEmpty;
 
-  bool hasOnePositionalArgumentThatMatches(bool f(T type)) {
-    return named.isEmpty && positional.length == 1 && f(positional[0]);
-  }
-
   void forEach(void f(T type)) {
     positional.forEach(f);
     named.values.forEach(f);