Adjusts dart2js backend to handle method type arguments.

tests/language/generic_methods_new_test.dart

+// 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.
+//
+// DartOptions=--generic-method-syntax
+
+/// Dart test on the usage of method type arguments in object creation. With
+/// '--generic-method-syntax', the type argument is available at runtime,
+/// but erased to `dynamic`.
+
+library generic_methods_new_test;
+
+import "package:expect/expect.dart";
+
+class C<E> {
+  E e;
+  C(this.e);
+}
+
+C<T> f1<T>(T t) => new C<T>(t);
+
+List<T> f2<T>(T t) => <T>[t];
+
+main() {
+  C c = f1<int>(42);
+  List i = f2<String>("Hello!");
+  Expect.isTrue(c is C<int> && c is C<String>); // C<dynamic>.
+  Expect.isTrue(i is List<String> && i is List<int>); // List<dynamic>.
+  Expect.equals(c.e, 42);
+  Expect.equals(i[0], "Hello!");
+}