Insert covariance checks in strong mode.

pkg/kernel/testcases/input/covariant_generic.dart

Index: pkg/kernel/testcases/input/covariant_generic.dart
diff --git a/pkg/kernel/testcases/input/covariant_generic.dart b/pkg/kernel/testcases/input/covariant_generic.dart
new file mode 100644
index 0000000000000000000000000000000000000000..a0234a681ce5d20e6a1c99f836c35cb12cce921a
--- /dev/null
+++ b/pkg/kernel/testcases/input/covariant_generic.dart
@@ -0,0 +1,45 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+typedef void Callback<T>(T x);
+
+class Foo<T> {
+  final T finalField;
+  final Callback<T> callbackField;
+
+  T mutableField;
+  Callback<T> mutableCallbackField;
+
+  Foo(this.finalField, this.callbackField);
+
+  void method(T x) {}
+
+  set setter(T x) {}
+
+  void withCallback(Callback<T> callback) {
+    callback(finalField);
+  }
+}
+
+main() {
+  Foo<int> fooInt = new Foo<int>(1, (int x) {});
+
+  fooInt.method(3);
+  fooInt.setter = 3;
+  fooInt.withCallback((int x) {});
+  fooInt.withCallback((num x) {});
+  fooInt.mutableField = 3;
+  fooInt.mutableCallbackField = (int x) {};
+
+  Foo<num> fooNum = fooInt;
+  fooNum.method(3);
+  fooNum.method(2.5);
+  fooNum.setter = 3;
+  fooNum.setter = 2.5;
+  fooNum.withCallback((num x) {});
+  fooNum.mutableField = 3;
+  fooNum.mutableField = 2.5;
+  fooNum.mutableCallbackField(3);
+  fooNum.mutableCallbackField(2.5);
+  fooNum.mutableCallbackField = (num x) {};
+}