Print debug info in generate_json_test.

pkg/docgen/test/generate_json_test.dart

Index: pkg/docgen/test/generate_json_test.dart
diff --git a/pkg/docgen/test/generate_json_test.dart b/pkg/docgen/test/generate_json_test.dart
index 68a3a12b2b28b65dcc03241695aa382593129e96..a852101843f1b3d16ecc92ce2193b6729338acab 100644
--- a/pkg/docgen/test/generate_json_test.dart
+++ b/pkg/docgen/test/generate_json_test.dart
@@ -39,7 +39,14 @@ void main() {
         d.matcherFile('test_lib.B.json', isJsonMap),
         d.matcherFile('test_lib.C.json', isJsonMap),
         d.matcherFile('test_lib.json', isJsonMap),
-    ]).validate();
+    ]).validate()
+      // TODO(ajohnsen): Remove once the issue is resolved.
+      .catchError((e, s) {
+        print(e);
+        print(s);
+        print(d.describe());
+        exit(1);
+      });
 
   });
 }