Add MediaGpuChannelManager::LookupChannel().

media/gpu/ipc/service/media_gpu_channel.cc

Index: media/gpu/ipc/service/media_gpu_channel.cc
diff --git a/media/gpu/ipc/service/media_gpu_channel.cc b/media/gpu/ipc/service/media_gpu_channel.cc
index 6a53bd05b16a2551cc590706b55dc24667091c33..ef81181eafc249dd762a9b72cd93ddbe53e63e3d 100644
--- a/media/gpu/ipc/service/media_gpu_channel.cc
+++ b/media/gpu/ipc/service/media_gpu_channel.cc
@@ -89,9 +89,10 @@ class MediaGpuChannelFilter : public IPC::MessageFilter {
   base::UnguessableToken channel_token_;
 };
 
-MediaGpuChannel::MediaGpuChannel(gpu::GpuChannel* channel) : channel_(channel) {
-  channel_->AddFilter(
-      new MediaGpuChannelFilter(base::UnguessableToken::Create()));
+MediaGpuChannel::MediaGpuChannel(gpu::GpuChannel* channel,
+                                 base::UnguessableToken channel_token)
+    : channel_(channel) {
+  channel_->AddFilter(new MediaGpuChannelFilter(std::move(channel_token)));
 }
 
 MediaGpuChannel::~MediaGpuChannel() {}