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 692676b58445d4f8d4c11e4d0109e089604a7e89..b5569e757c0f88bd4f1c5131d2f9f655db2826bd 100644
--- a/pkg/compiler/lib/src/js_emitter/runtime_type_generator.dart
+++ b/pkg/compiler/lib/src/js_emitter/runtime_type_generator.dart
@@ -128,12 +128,11 @@ class RuntimeTypeGenerator {
       if (!method.isAbstract) {
         ClosureRepresentationInfo closureData =
             _closureDataLookup.getClosureRepresentationInfo(method);
-        if (closureData != null) {
+        if (closureData.isClosure && closureData.thisLocal != null) {

[Siggi Cherem (dart-lang), 2017/06/20 00:30:22]

is closureData never null now? Will it ever be the case that isClosure is false,
but thisLocal is true? If not, we could write this as:

if (closureData?.thisLocal != null) { ... }

           ClosureFieldElement thisLocal = closureData.thisFieldEntity;
-          if (thisLocal != null) {
-            jsAst.Name thisName = _namer.instanceFieldPropertyName(thisLocal);
-            thisAccess = js('this.#', thisName);
-          }
+          assert(thisLocal != null);
+          jsAst.Name thisName = _namer.instanceFieldPropertyName(thisLocal);
+          thisAccess = js('this.#', thisName);
         }
       }