add tests to demonstrate missing generic function subtype logic

pkg/analyzer/test/src/task/strong/checker_test.dart

Index: pkg/analyzer/test/src/task/strong/checker_test.dart
diff --git a/pkg/analyzer/test/src/task/strong/checker_test.dart b/pkg/analyzer/test/src/task/strong/checker_test.dart
index a1170ef89c78c06f4e35dec9b6aff2a07721aa80..f64589f0f9939891eea5a3775b30a71174425225 100644
--- a/pkg/analyzer/test/src/task/strong/checker_test.dart
+++ b/pkg/analyzer/test/src/task/strong/checker_test.dart
@@ -1351,6 +1351,51 @@ void main() {
        '''
   });
 
+  testChecker('generic class method override', {
+    '/main.dart': '''
+          class A {}
+          class B extends A {}
+
+          class Base<T extends B> {
+            T foo() => null;
+          }
+
+          class Derived<S extends A> extends Base<B> {
+            /*severe:INVALID_METHOD_OVERRIDE*/S foo() => null;
+          }
+
+          class Derived2<S extends B> extends Base<B> {
+            S foo() => null;
+          }
+       '''
+  });
+
+  testChecker('generic method override', {
+    '/main.dart': '''
+          class Future<T> {
+            /*=S*/ then/*<S>*/(/*=S*/ onValue(T t)) => null;
+          }
+
+          // These work because they're exactly equal FunctionTypes
+          class DerivedFuture<T> extends Future<T> {
+            /*=S*/ then/*<S>*/(/*=S*/ onValue(T t)) => null;
+          }
+
+          class DerivedFuture2<A> extends Future<A> {
+            /*=B*/ then/*<B>*/(/*=B*/ onValue(A a)) => null;
+          }
+
+          // These don't work but should.
+          class DerivedFuture3<T> extends Future<T> {
+            /*=/*severe:INVALID_METHOD_OVERRIDE*/S*/ then/*<S>*/(Object onValue(T t)) => null;

[Leaf, 2015/12/07 21:44:54]

you can say /*severe:INVALID_METHOD_OVERRIDE should be pass*/ .  

[Jennifer Messerly, 2015/12/07 22:29:30]

Done.

+          }
+
+          class DerivedFuture4<A> extends Future<A> {
+            /*=/*severe:INVALID_METHOD_OVERRIDE*/B*/ then/*<B>*/(Object onValue(A a)) => null;
+          }
+       '''
+  });
+
   testChecker('unary operators', {
     '/main.dart': '''
       class A {