Mojo C++ bindings: support attaching context object for StructTraits.

mojo/public/cpp/bindings/tests/struct_with_traits_impl_traits.h

 // Copyright 2016 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.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_TESTS_STRUCT_WITH_TRAITS_IMPL_TRAITS_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_TESTS_STRUCT_WITH_TRAITS_IMPL_TRAITS_H_
 
 #include <stdint.h>
 
 #include <string>
 #include <vector>
 
 #include "base/strings/string_piece.h"
 #include "mojo/public/cpp/bindings/struct_traits.h"
 #include "mojo/public/cpp/bindings/tests/struct_with_traits_impl.h"
 #include "mojo/public/interfaces/bindings/tests/struct_with_traits.mojom.h"
 
 namespace mojo {
 
 template <>
 struct StructTraits<test::NestedStructWithTraits,
                     test::NestedStructWithTraitsImpl> {
+  static void* SetUpContext(const test::NestedStructWithTraitsImpl& input);
+  static void TearDownContext(const test::NestedStructWithTraitsImpl& input,
+                              void* context);
+
+  static int32_t value(const test::NestedStructWithTraitsImpl& input,
+                       void* context);
+
   static bool Read(test::NestedStructWithTraitsDataView data,
                    test::NestedStructWithTraitsImpl* output);
-  static int32_t value(const test::NestedStructWithTraitsImpl& input) {
-    return input.value;
-  }
 };
 
 template <>
 struct StructTraits<test::StructWithTraits, test::StructWithTraitsImpl> {
   // Deserialization to test::StructTraitsImpl.
   static bool Read(test::StructWithTraitsDataView data,
                    test::StructWithTraitsImpl* out);
 
   // Fields in test::StructWithTraits.
   // See src/mojo/public/interfaces/bindings/tests/struct_with_traits.mojom.
@@ skipping 29 matching lines @@
 
   static const std::vector<test::NestedStructWithTraitsImpl>& f_struct_array(
       const test::StructWithTraitsImpl& value) {
     return value.get_struct_array();
   }
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_TESTS_STRUCT_WITH_TRAITS_IMPL_TRAITS_H_