mobile/bind: add integration test for CL 19417

Change-Id: I6a2cab4ca9b5bd61db51d08966da19fdfb07c344
Reviewed-on: https://go-review.googlesource.com/19463
Reviewed-by: David Crawshaw <crawshaw@golang.org>

bind/java/SeqTest.java

@@ -374,6 +374,10 @@ public class SeqTest extends AndroidTestCase {
     assertEquals("want Node A points to Node B", "A:B:<end>", got);
   }
 
+  public void testImplementsInterface() {
+    Testpkg.Interface intf = Testpkg.NewConcrete();
+  }
+
   public void testErrorField() {
     final String want = "an error message";
     Testpkg.Node n = Testpkg.NewNode("ErrTest");