Add an issue reference to a TODO in barback.

pkg/barback/lib/src/phase_input.dart

Index: pkg/barback/lib/src/phase_input.dart
diff --git a/pkg/barback/lib/src/phase_input.dart b/pkg/barback/lib/src/phase_input.dart
index 2168f03b9ee5c19f9e36ee4ce5f81b868e342c42..63aa1806508045a33cccd9312d8de2245927405f 100644
--- a/pkg/barback/lib/src/phase_input.dart
+++ b/pkg/barback/lib/src/phase_input.dart
@@ -199,7 +199,7 @@ class PhaseInput {
         if (!transformers.contains(transform.transformer)) return false;
 
         // TODO(rnystrom): Catch all errors from isPrimary() and redirect to
-        // results.
+        // results (issue 16162).
         return transform.transformer.isPrimary(asset);
       }).then((isPrimary) {
         if (isPrimary) return;