Perform substitution on the unaliased type of a typedef.

sdk/lib/_internal/compiler/implementation/dart_types.dart

Index: sdk/lib/_internal/compiler/implementation/dart_types.dart
diff --git a/sdk/lib/_internal/compiler/implementation/dart_types.dart b/sdk/lib/_internal/compiler/implementation/dart_types.dart
index 285ef1a3e0c6aebbf61faa528a763205f76d1057..b43de387745253218013dbe7fd928b52fce58523 100644
--- a/sdk/lib/_internal/compiler/implementation/dart_types.dart
+++ b/sdk/lib/_internal/compiler/implementation/dart_types.dart
@@ -622,8 +622,9 @@ class TypedefType extends DartType {
   DartType unalias(Compiler compiler) {
     // TODO(ahe): This should be [ensureResolved].
     compiler.resolveTypedef(element);
-    // TODO(johnniwinther): Perform substitution on the unaliased type.
-    return element.alias.unalias(compiler);
+    DartType definition = element.alias.unalias(compiler);
+    TypedefType declaration = element.computeType(compiler);
+    return definition.subst(typeArguments, declaration.typeArguments);
   }
 
   String toString() {