Add validation logic for non-nullable types.

mojo/public/interfaces/bindings/tests/validation_test_interfaces.mojom

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 
 [JavaPackage="org.chromium.mojo.bindings.test.mojom.mojo"]
 module mojo.test {
 
 struct StructA {
   uint64 i;
@@ skipping 22 matching lines @@
 
 interface ConformanceTestInterface {
   Method0(float param0);
   Method1(StructA param0);
   Method2(StructB param0, StructA param1);
   Method3(bool[] param0);
   Method4(StructC param0, uint8[] param1);
   Method5(StructE param0, handle<data_pipe_producer> param1);
   Method6(uint8[][] param0);
   Method7(StructF param0, uint8[5] param1);
+  Method8(string[]?[] param0);
+  Method9(handle?[][]? param0);
 };
 
 struct BasicStruct {
   int32 a;
 };
 
 [Client=IntegrationTestInterface2]
 interface IntegrationTestInterface1 {
   Method0(BasicStruct param0);
 };
 
 [Client=IntegrationTestInterface1]
 interface IntegrationTestInterface2 {
   Method0() => (uint8[] param0);
 };
 
 }