Setup DiscardableMemory in the ash process

ui/aura/mus/window_tree_client.h

Index: ui/aura/mus/window_tree_client.h
diff --git a/ui/aura/mus/window_tree_client.h b/ui/aura/mus/window_tree_client.h
index 63073714c818f062032f27e0558111c8cbff5323..9524d444485b343aad11275236fcb3ff877422e6 100644
--- a/ui/aura/mus/window_tree_client.h
+++ b/ui/aura/mus/window_tree_client.h
@@ -30,6 +30,14 @@
 #include "ui/aura/mus/window_manager_delegate.h"
 #include "ui/aura/mus/window_tree_host_mus_delegate.h"
 
+namespace base {
+class Thread;
+}
+
+namespace discardable_memory {
+class ClientDiscardableSharedMemoryManager;
+}
+
 namespace display {
 class Display;
 }
@@ -543,9 +551,15 @@ class AURA_EXPORT WindowTreeClient
 
   base::ObserverList<WindowTreeClientTestObserver> test_observers_;
 
+  // IO thread for GPU and discardable shared memory IPC.
+  std::unique_ptr<base::Thread> io_thread_;
+
   std::unique_ptr<ui::Gpu> gpu_;
   std::unique_ptr<MusContextFactory> compositor_context_factory_;
 
+  std::unique_ptr<discardable_memory::ClientDiscardableSharedMemoryManager>
+      discardable_shared_memory_manager_;
+
   // If |compositor_context_factory_| is installed on Env, then this is the
   // ContextFactory that was set on Env originally.
   ui::ContextFactory* initial_context_factory_ = nullptr;