[mojo] Initialize MojoCreateSharedBufferOptions struct size.

mojo/edk/js/core.cc

 // 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.
 
 #include "mojo/edk/js/core.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include "base/bind.h"
@@ skipping 277 matching lines @@
   return gin::Converter<gin::Handle<mojo::edk::js::HandleWrapper>>::FromV8(
       args->isolate(), val, &ignore_handle);
 }
 
 gin::Dictionary CreateSharedBuffer(const gin::Arguments& args,
                                    uint64_t num_bytes,
                                    MojoCreateSharedBufferOptionsFlags flags) {
   gin::Dictionary dictionary = gin::Dictionary::CreateEmpty(args.isolate());
   MojoHandle handle = MOJO_HANDLE_INVALID;
   MojoCreateSharedBufferOptions options;
+  // The |flags| is mandatory parameter for CreateSharedBuffer, and it will
+  // be always initialized in MojoCreateSharedBufferOptions struct. For
+  // forward compatibility, set struct_size to be 8 bytes (struct_size + flags),
+  // so that validator will only check the field that is set.
+  options.struct_size = 8;
   options.flags = flags;
   MojoResult result = MojoCreateSharedBuffer(&options, num_bytes, &handle);
   if (result != MOJO_RESULT_OK) {
     dictionary.Set("result", result);
     return dictionary;
   }
 
   dictionary.Set("result", result);
   dictionary.Set("handle", mojo::Handle(handle));
 
   return dictionary;
 }
 
 gin::Dictionary DuplicateBufferHandle(
     const gin::Arguments& args,
     mojo::Handle handle,
     MojoDuplicateBufferHandleOptionsFlags flags) {
   gin::Dictionary dictionary = gin::Dictionary::CreateEmpty(args.isolate());
   MojoHandle duped = MOJO_HANDLE_INVALID;
   MojoDuplicateBufferHandleOptions options;
   // The |flags| is mandatory parameter for DuplicateBufferHandle, and it will
-  // be always initialized in MojoDuplicateBufferHandleOptions struct. For now,
-  // since the struct has only one options field (flags), set struct_size to be
-  // equal to the size of MojoDuplicateBufferHandleOptions.
-  options.struct_size =
-      static_cast<uint32_t>(sizeof(MojoDuplicateBufferHandleOptions));
+  // be always initialized in MojoDuplicateBufferHandleOptions struct. For
+  // forward compatibility, set struct_size to be 8 bytes (struct_size + flags),
+  // so that validator will only check the field that is set.
+  options.struct_size = 8;
   options.flags = flags;
   MojoResult result =
       MojoDuplicateBufferHandle(handle.value(), &options, &duped);
   if (result != MOJO_RESULT_OK) {
     dictionary.Set("result", result);
     return dictionary;
   }
 
   dictionary.Set("result", result);
   dictionary.Set("handle", mojo::Handle(duped));
@@ skipping 130 matching lines @@
 
     data->SetObjectTemplate(&g_wrapper_info, templ);
   }
 
   return templ->NewInstance();
 }
 
 }  // namespace js
 }  // namespace edk
 }  // namespace mojo