Add MediaGpuChannelManager::LookupChannel().

media/gpu/ipc/service/media_gpu_channel_manager.h

Index: media/gpu/ipc/service/media_gpu_channel_manager.h
diff --git a/media/gpu/ipc/service/media_gpu_channel_manager.h b/media/gpu/ipc/service/media_gpu_channel_manager.h
index 01aa42e84bd0a8510b12a54f2b0729a5666ae618..8cc3f2ff4b7a236ebc298622ec0366ff43898620 100644
--- a/media/gpu/ipc/service/media_gpu_channel_manager.h
+++ b/media/gpu/ipc/service/media_gpu_channel_manager.h
@@ -12,11 +12,13 @@
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
+#include "base/unguessable_token.h"
 #include "ipc/ipc_listener.h"
 #include "ipc/ipc_sender.h"
 #include "media/video/video_decode_accelerator.h"
 
 namespace gpu {
+class GpuChannel;
 class GpuChannelManager;
 }
 
@@ -34,10 +36,15 @@ class MediaGpuChannelManager
   void RemoveChannel(int32_t client_id);
   void DestroyAllChannels();
 
+  // TODO(sandersd): Should we expose the MediaGpuChannel instead?
+  gpu::GpuChannel* LookupChannel(const base::UnguessableToken& channel_token);
+
  private:
   gpu::GpuChannelManager* const channel_manager_;
   std::unordered_map<int32_t, std::unique_ptr<MediaGpuChannel>>
       media_gpu_channels_;
+  std::map<base::UnguessableToken, int32_t> token_to_channel_;
+  std::map<int32_t, base::UnguessableToken> channel_to_token_;
   DISALLOW_COPY_AND_ASSIGN(MediaGpuChannelManager);
 };