Support `void` as generic argument.

pkg/compiler/lib/src/resolution/resolution.dart

Index: pkg/compiler/lib/src/resolution/resolution.dart
diff --git a/pkg/compiler/lib/src/resolution/resolution.dart b/pkg/compiler/lib/src/resolution/resolution.dart
index 94c8adc6bd06ffc90069f9951c09729b72d79aed..b48bdeaa2be4e3604f1a7a19ac288783af2cffab 100644
--- a/pkg/compiler/lib/src/resolution/resolution.dart
+++ b/pkg/compiler/lib/src/resolution/resolution.dart
@@ -441,15 +441,6 @@ class ResolverTask extends CompilerTask {
 
   ResolutionDartType resolveTypeAnnotation(
       Element element, TypeAnnotation annotation) {
-    ResolutionDartType type = _resolveReturnType(element, annotation);
-    if (type.isVoid) {
-      reporter.reportErrorMessage(annotation, MessageKind.VOID_NOT_ALLOWED);
-    }
-    return type;
-  }
-
-  ResolutionDartType _resolveReturnType(
-      Element element, TypeAnnotation annotation) {
     if (annotation == null) return const ResolutionDynamicType();
     ResolutionDartType result =
         visitorFor(element).resolveTypeAnnotation(annotation);