Fix getSetterType in presence of metadata

pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/classes.dart

Index: pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/classes.dart
diff --git a/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/classes.dart b/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/classes.dart
index 69281b050e70a008d938238b3818fbf5cadd69f0..c7b57180345c52a334056562f02a5b89a16c61ca 100644
--- a/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/classes.dart
+++ b/pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/classes.dart
@@ -237,6 +237,14 @@ getSetterType(type, name) {
     if (type != null) {
       // TODO(jmesserly): it would be nice not to encode setters with a full
       // function type.
+      if (JS('bool', '# instanceof Array', type)) {
+        // The type has metadata attached.  Pull out just the type.
+        // TODO(vsm): Come up with a more robust encoding for this or remove
+        // if we can deprecate mirrors.
+        // Essentially, we've got a FunctionType or a
+        // [FunctionType, metadata1, ..., metadataN].
+        type = JS('', '#[0]', type);
+      }
       return JS('', '#.args[0]', type);
     }
   }