dart2js cps_ir: Use interceptors for is-checks (version 2)

sdk/lib/_internal/js_runtime/lib/js_rti.dart

Index: sdk/lib/_internal/js_runtime/lib/js_rti.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/js_rti.dart b/sdk/lib/_internal/js_runtime/lib/js_rti.dart
index 60af58d2331934fe80ff2803951787b68ab29902..65ae2576c9ee0b882bfd868eeb21c4371b3ebbf0 100644
--- a/sdk/lib/_internal/js_runtime/lib/js_rti.dart
+++ b/sdk/lib/_internal/js_runtime/lib/js_rti.dart
@@ -237,11 +237,17 @@ substitute(var substitution, var arguments) {
   assert(arguments == null || isJsArray(arguments));
   if (isJsFunction(substitution)) {
     substitution = invoke(substitution, arguments);
-    if (substitution == null || isJsArray(substitution)) {
-      arguments = substitution;
-    } else if (isJsFunction(substitution)) {
+    if (substitution == null) return substitution;
+    if (isJsArray(substitution)) {
+      // Substitutions are generated too late to mark Array as used, so use a
+      // tautological JS 'cast' to mark Array as used. This is needed only in
+      // some tiny tests where the substition is the only thing that creates an
+      // Array.
+      return JS('JSArray', '#', substitution);
+    }
+    if (isJsFunction(substitution)) {
       // TODO(johnniwinther): Check if this is still needed.
-      arguments = invoke(substitution, arguments);
+      return invoke(substitution, arguments);
     }
   }
   return arguments;