Mojo C++ bindings: fix inlined union validation.

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 38 matching lines @@
   ENUM_A_1
 };
 
 [Extensible]
 enum EnumB {
   ENUM_B_0,
   ENUM_B_1,
   ENUM_B_2
 };
 
+union UnionA {
+  StructA struct_a;
+  bool b;
+};
+
 // This interface is used for testing bounds-checking in the mojom
 // binding code. If you add a method please update the files
 // ./data/validation/boundscheck_*. If you add a response please update
 // ./data/validation/resp_boundscheck_*.
 interface BoundsCheckTestInterface {
   Method0(uint8 param0) => (uint8 param0);
   Method1(uint8 param0);
 };
 
 interface ConformanceTestInterface {
   Method0(float param0);
   Method1(StructA param0);
   Method2(StructB param0, StructA param1);
   Method3(array<bool> param0);
   Method4(StructC param0, array<uint8> param1);
   Method5(StructE param0, handle<data_pipe_producer> param1);
   Method6(array<array<uint8>> param0);
   Method7(StructF param0, array<array<uint8, 3>?, 2> param1);
   Method8(array<array<string>?> param0);
   Method9(array<array<handle?>>? param0);
   Method10(map<string, uint8> param0);
   Method11(StructG param0);
   Method12(float param0) => (float param0);
   Method13(InterfaceA? param0, uint32 param1, InterfaceA? param2);
   Method14(EnumA param0, EnumB param1);
   Method15(array<EnumA>? param0, array<EnumB>? param1);
   Method16(map<EnumA, EnumA>? param0);
   Method17(array<InterfaceA> param0);
+  Method18(UnionA? param0);
 };
 
 struct BasicStruct {
   int32 a;
 };
 
 interface IntegrationTestInterface {
   Method0(BasicStruct param0) => (array<uint8> param0);
 };
 
 // An enum generates a enum-value validation function, so we want to test it.
 // E.g., valid enum values for this enum should be:  -3, 0, 1, 10
 enum BasicEnum {
   A,
   B,
   C = A,
   D = -3,
   E = 0xA
 };
 
 // The enum validation function should be generated within the scope of this
 // struct.
 struct StructWithEnum {
   enum EnumWithin {
     A, B, C, D
   };
 };