Setup DiscardableMemory in the ash process

ui/aura/mus/window_tree_client.cc

Index: ui/aura/mus/window_tree_client.cc
diff --git a/ui/aura/mus/window_tree_client.cc b/ui/aura/mus/window_tree_client.cc
index 82f54f0d6d4d97dc79c56cebfb063cc8c2b5661e..9c59dbbc1a4e5db966e0ecfd7dbaa5215d7031fe 100644
--- a/ui/aura/mus/window_tree_client.cc
+++ b/ui/aura/mus/window_tree_client.cc
@@ -13,6 +13,8 @@
 #include "base/auto_reset.h"
 #include "base/bind.h"
 #include "base/memory/ptr_util.h"
+#include "base/threading/thread.h"
+#include "components/discardable_memory/client/client_discardable_shared_memory_manager.h"
 #include "mojo/public/cpp/bindings/map.h"
 #include "services/service_manager/public/cpp/connector.h"
 #include "services/ui/common/accelerator_util.h"
@@ -194,17 +196,35 @@ WindowTreeClient::WindowTreeClient(
   if (window_manager_delegate)
     window_manager_delegate->SetWindowManagerClient(this);
   if (connector) {  // |connector| can be null in tests.
-    gpu_ = ui::Gpu::Create(connector, std::move(io_task_runner));
+    if (!io_task_runner) {

[James Cook, 2017/03/13 21:17:15]

nit: Maybe document when io_task_runner can be null. Tests? Certain mus apps?

[Peng, 2017/03/14 15:03:14]

Done

+      io_thread_ = base::MakeUnique<base::Thread>("IOThread");
+      base::Thread::Options thread_options(base::MessageLoop::TYPE_IO, 0);
+      thread_options.priority = base::ThreadPriority::NORMAL;
+      CHECK(io_thread_->StartWithOptions(thread_options));
+      io_task_runner = io_thread_->task_runner();
+    }
+
+    gpu_ = ui::Gpu::Create(connector, io_task_runner);
     compositor_context_factory_ =
         base::MakeUnique<MusContextFactory>(gpu_.get());
     initial_context_factory_ = Env::GetInstance()->context_factory();
     Env::GetInstance()->set_context_factory(compositor_context_factory_.get());
+
+    discardable_memory::mojom::DiscardableSharedMemoryManagerPtr manager_ptr;
+    connector->BindInterface(ui::mojom::kServiceName, &manager_ptr);
+    discardable_shared_memory_manager_ = base::MakeUnique<
+        discardable_memory::ClientDiscardableSharedMemoryManager>(
+        std::move(manager_ptr), std::move(io_task_runner));
+    base::DiscardableMemoryAllocator::SetInstance(
+        discardable_shared_memory_manager_.get());
   }
 }
 
 WindowTreeClient::~WindowTreeClient() {
   in_destructor_ = true;
 
+  base::DiscardableMemoryAllocator::SetInstance(nullptr);
+
   for (WindowTreeClientObserver& observer : observers_)
     observer.OnWillDestroyClient(this);