Add IPC to query capabilities of video input devices.

content/browser/media/media_devices_util.h

+// Copyright 2017 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 CONTENT_BROWSER_MEDIA_MEDIA_DEVICES_UTIL_H_
+#define CONTENT_BROWSER_MEDIA_MEDIA_DEVICES_UTIL_H_
+
+#include <string>
+
+#include "base/callback.h"
+#include "content/common/content_export.h"
+#include "content/common/media/media_devices.h"
+
+namespace content {
+
+// Returns the ID of the user-default device ID via |callback|.
+// If no such device ID can be found, |callback| receives an empty string.
+void CONTENT_EXPORT GetDefaultMediaDeviceID(
+    MediaDeviceType device_type,
+    int render_process_id,
+    int render_frame_id,
+    const base::Callback<void(const std::string&)>& callback);
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_MEDIA_MEDIA_DEVICES_UTIL_H_