Migrate MediaDevices.enumerateDevices to Mojo

content/common/media/media_devices_param_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.
+
+// Multiply-included IPC traits file, hence no include guard.

[hta - Chromium, 2016/09/30 08:38:12]

I'm a bit surprised to see this IPC traits file in the mojom-based solution. Why
is it needed?

[Guido Urdaneta, 2016/10/07 17:07:13]

Because the MediaDeviceInfo type we are using is a regular C++ struct and we
need to define a way to serialize it for IPC purposes.

The choices are:
1. Define a Mojo struct that replaces MediaDeviceInfo and use it everywhere,
even in things not concerned with IPC.
2. Define a Mojo struct as in (1), but instead of replacing
content::MediaDeviceInfo,  define a mapping from the native version to the mojo
one.
3. Use IPC_ macros to generate serialization code for MediaDeviceInfo.
4. Manually write the serialization code for MediaDeviceInfo (same code
generated by the IPC_ macros)

As of now, the most straightforward choice is (3).
We might want to invoke this directly from Blink at some point. In that case
we'll probably have to go with (1) or (2).

+
+#include "content/common/content_export.h"
+#include "content/common/media/media_devices.h"
+#include "ipc/ipc_message_macros.h"
+
+#undef IPC_MESSAGE_EXPORT
+#define IPC_MESSAGE_EXPORT CONTENT_EXPORT
+
+IPC_ENUM_TRAITS_MAX_VALUE(content::MediaDeviceType,
+                          content::NUM_MEDIA_DEVICE_TYPES - 1)
+
+IPC_STRUCT_TRAITS_BEGIN(content::MediaDeviceInfo)
+  IPC_STRUCT_TRAITS_MEMBER(device_id)
+  IPC_STRUCT_TRAITS_MEMBER(label)
+  IPC_STRUCT_TRAITS_MEMBER(group_id)
+IPC_STRUCT_TRAITS_END()