Support `void` as generic argument.

pkg/compiler/lib/src/js_backend/runtime_types.dart

Index: pkg/compiler/lib/src/js_backend/runtime_types.dart
diff --git a/pkg/compiler/lib/src/js_backend/runtime_types.dart b/pkg/compiler/lib/src/js_backend/runtime_types.dart
index e6e5a5d4faf752bc5c0ffdd7f04806f3e228feef..533eb0507a625e3dc75aacc7befd744778f1dc61 100644
--- a/pkg/compiler/lib/src/js_backend/runtime_types.dart
+++ b/pkg/compiler/lib/src/js_backend/runtime_types.dart
@@ -98,6 +98,9 @@ abstract class RuntimeTypesEncoder {
       [ShouldEncodeTypedefCallback shouldEncodeTypedef]);
 
   String getTypeRepresentationForTypeConstant(ResolutionDartType type);
+
+  jsAst.Expression get voidRti;
+  jsAst.Template get templateForIsVoidRti;
 }
 
 class _RuntimeTypes implements RuntimeTypes {
@@ -771,6 +774,14 @@ class _RuntimeTypesEncoder implements RuntimeTypesEncoder {
     }
     return true;
   }
+
+  @override
+  jsAst.Expression get voidRti => js('1');
+
+  @override
+  jsAst.Template get templateForIsVoidRti {
+    return jsAst.js.expressionTemplateFor("# === 1");
+  }
 }
 
 class TypeRepresentationGenerator implements DartTypeVisitor {
@@ -802,7 +813,7 @@ class TypeRepresentationGenerator implements DartTypeVisitor {
     return representation;
   }
 
-  jsAst.Expression getJavaScriptClassName(Element element) {
+  jsAst.Expression getJavaScriptClassName(Entity element) {
     return backend.emitter.typeAccess(element);
   }
 
@@ -864,9 +875,7 @@ class TypeRepresentationGenerator implements DartTypeVisitor {
     // Type representations for functions have a property which is a tag marking
     // them as function types. The value is not used, so '1' is just a dummy.
     addProperty(namer.functionTypeTag, js.number(1));
-    if (type.returnType.isVoid) {
-      addProperty(namer.functionTypeVoidReturnTag, js('true'));
-    } else if (!type.returnType.treatAsDynamic) {
+    if (!type.returnType.treatAsDynamic) {
       addProperty(namer.functionTypeReturnTypeTag, visit(type.returnType));
     }
     if (!type.parameterTypes.isEmpty) {
@@ -898,8 +907,7 @@ class TypeRepresentationGenerator implements DartTypeVisitor {
   }
 
   visitVoidType(ResolutionVoidType type, _) {
-    // TODO(ahe): Reify void type ("null" means "dynamic").
-    return js('null');
+    return backend.rtiEncoder.voidRti;
   }
 
   visitTypedefType(ResolutionTypedefType type, _) {