Begin writing tests of the runtime checks needed for Dart 2.0 soundness.

pkg/front_end/testcases/runtime_checks/covariant_generic_method_type_parameter.dart.direct.expect

+library test;
+import self as self;
+import "dart:core" as core;
+
+class C<T extends core::Object> extends core::Object {
+  default constructor •() → void
+    : super core::Object::•()
+    ;
+  method f<U extends self::C::T>(self::C::f::U x) → void {}
+  method g1<U extends self::C::T>() → void {
+    this.f<self::C::g1::U>(1.5);
+  }
+}
+static method g2(self::C<core::Object> c) → void {
+  c.f<core::num>(1.5);
+}
+static method test() → void {
+  new self::C::•<core::int>().g1<core::num>();
+  self::g2(new self::C::•<core::int>());
+}
+static method main() → void {}