Require legacy form of type parameters in factories and report errors if a factory class does not...

tests/language/src/NonParameterizedFactoryTest.dart

Index: tests/language/src/NonParameterizedFactoryTest.dart
===================================================================
--- tests/language/src/NonParameterizedFactoryTest.dart	(revision 1463)
+++ tests/language/src/NonParameterizedFactoryTest.dart	(working copy)
@@ -7,12 +7,13 @@
   Interface.withArg(T value);
 }
 
+// A factory must be parametrized. Use legacy form.
 class Factory {
-  factory Interface() {
+  factory Interface<T>() {
     return null;
   }
 
-  factory Interface.withArg(value) {
+  factory Interface<T>.withArg(value) {
     return null;
   }
 }