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 9b54dcd33f539775817e284b82318634206d2440..6343d7c529c820d6b40c46b4bce91c7e03763c5a 100644
--- a/pkg/compiler/lib/src/js_backend/runtime_types.dart
+++ b/pkg/compiler/lib/src/js_backend/runtime_types.dart
@@ -134,6 +134,8 @@ abstract class RuntimeTypesEncoder {
       [ShouldEncodeTypedefCallback shouldEncodeTypedef]);
 
   String getTypeRepresentationForTypeConstant(ResolutionDartType type);
+
+  jsAst.Template get templateForIsVoidRti;
 }
 
 /// Common functionality for [_RuntimeTypesNeedBuilder] and [_RuntimeTypes].
@@ -770,10 +772,10 @@ class _RuntimeTypes extends _RuntimeTypesBase
 class _RuntimeTypesEncoder implements RuntimeTypesEncoder {
   final Namer namer;
   final CommonElements commonElements;
-  final TypeRepresentationGenerator _representationGenerator;
+  final _TypeRepresentationGenerator _representationGenerator;
 
   _RuntimeTypesEncoder(this.namer, this.commonElements)
-      : _representationGenerator = new TypeRepresentationGenerator(namer);
+      : _representationGenerator = new _TypeRepresentationGenerator(namer);
 
   @override
   bool isSimpleFunctionType(ResolutionFunctionType type) {
@@ -926,15 +928,22 @@ class _RuntimeTypesEncoder implements RuntimeTypesEncoder {
     String arguments = new List.filled(variables.length, 'dynamic').join(', ');
     return '$name<$arguments>';
   }
+
+  static jsAst.Expression get _voidRti => js('1');
+
+  @override
+  jsAst.Template get templateForIsVoidRti {
+    return jsAst.js.expressionTemplateFor("# === 1");
+  }
 }
 
-class TypeRepresentationGenerator implements ResolutionDartTypeVisitor {
+class _TypeRepresentationGenerator implements ResolutionDartTypeVisitor {
   final Namer namer;
   OnVariableCallback onVariable;
   ShouldEncodeTypedefCallback shouldEncodeTypedef;
   Map<ResolutionTypeVariableType, jsAst.Expression> typedefBindings;
 
-  TypeRepresentationGenerator(this.namer);
+  _TypeRepresentationGenerator(this.namer);
 
   /**
    * Creates a type representation for [type]. [onVariable] is called to provide
@@ -1024,9 +1033,7 @@ class TypeRepresentationGenerator implements ResolutionDartTypeVisitor {
     // 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, emitter));
     }
@@ -1060,8 +1067,7 @@ class TypeRepresentationGenerator implements ResolutionDartTypeVisitor {
   }
 
   visitVoidType(ResolutionVoidType type, Emitter emitter) {
-    // TODO(ahe): Reify void type ("null" means "dynamic").
-    return js('null');
+    return _RuntimeTypesEncoder._voidRti;
   }
 
   visitTypedefType(ResolutionTypedefType type, Emitter emitter) {