Fix race in MediaDevicesPermissionChecker.

content/browser/renderer_host/media/media_devices_dispatcher_host.cc

Index: content/browser/renderer_host/media/media_devices_dispatcher_host.cc
diff --git a/content/browser/renderer_host/media/media_devices_dispatcher_host.cc b/content/browser/renderer_host/media/media_devices_dispatcher_host.cc
index 948b50255ca89e991a394680d752da8a2fd004f5..bba3ca9f8c5ef6f356c9d131085b5aa916e7226b 100644
--- a/content/browser/renderer_host/media/media_devices_dispatcher_host.cc
+++ b/content/browser/renderer_host/media/media_devices_dispatcher_host.cc
@@ -66,6 +66,7 @@ MediaDevicesDispatcherHost::MediaDevicesDispatcherHost(
       device_id_salt_(device_id_salt),
       group_id_salt_(ResourceContext::CreateRandomMediaDeviceIDSalt()),
       media_stream_manager_(media_stream_manager),
+      permission_checker_(base::MakeUnique<MediaDevicesPermissionChecker>()),
       weak_factory_(this) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
 }
@@ -100,7 +101,7 @@ void MediaDevicesDispatcherHost::EnumerateDevices(
   devices_to_enumerate[MEDIA_DEVICE_TYPE_VIDEO_INPUT] = request_video_input;
   devices_to_enumerate[MEDIA_DEVICE_TYPE_AUDIO_OUTPUT] = request_audio_output;
 
-  permission_checker_.CheckPermissions(
+  permission_checker_->CheckPermissions(
       devices_to_enumerate, render_process_id_, routing_id_, security_origin,
       base::Bind(&MediaDevicesDispatcherHost::DoEnumerateDevices,
                  weak_factory_.GetWeakPtr(), devices_to_enumerate,
@@ -108,9 +109,10 @@ void MediaDevicesDispatcherHost::EnumerateDevices(
 }
 
 void MediaDevicesDispatcherHost::SetPermissionChecker(
-    const MediaDevicesPermissionChecker& permission_checker) {
+    std::unique_ptr<MediaDevicesPermissionChecker> permission_checker) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
-  permission_checker_ = permission_checker;
+  DCHECK(permission_checker);
+  permission_checker_ = std::move(permission_checker);
 }
 
 void MediaDevicesDispatcherHost::DoEnumerateDevices(