Revert "Reapply "Minor adjustment to usage of the ClosureClassRepresentation interface.""

pkg/compiler/lib/src/js_emitter/runtime_type_generator.dart

Index: pkg/compiler/lib/src/js_emitter/runtime_type_generator.dart
diff --git a/pkg/compiler/lib/src/js_emitter/runtime_type_generator.dart b/pkg/compiler/lib/src/js_emitter/runtime_type_generator.dart
index b5569e757c0f88bd4f1c5131d2f9f655db2826bd..692676b58445d4f8d4c11e4d0109e089604a7e89 100644
--- a/pkg/compiler/lib/src/js_emitter/runtime_type_generator.dart
+++ b/pkg/compiler/lib/src/js_emitter/runtime_type_generator.dart
@@ -128,11 +128,12 @@ class RuntimeTypeGenerator {
       if (!method.isAbstract) {
         ClosureRepresentationInfo closureData =
             _closureDataLookup.getClosureRepresentationInfo(method);
-        if (closureData.isClosure && closureData.thisLocal != null) {
+        if (closureData != null) {
           ClosureFieldElement thisLocal = closureData.thisFieldEntity;
-          assert(thisLocal != null);
-          jsAst.Name thisName = _namer.instanceFieldPropertyName(thisLocal);
-          thisAccess = js('this.#', thisName);
+          if (thisLocal != null) {
+            jsAst.Name thisName = _namer.instanceFieldPropertyName(thisLocal);
+            thisAccess = js('this.#', thisName);
+          }
         }
       }