Setup DiscardableMemory in the ash process

ash/mus/window_manager_application.cc

Index: ash/mus/window_manager_application.cc
diff --git a/ash/mus/window_manager_application.cc b/ash/mus/window_manager_application.cc
index c3dbcf58f3767b43a26762b77312395bebfe22a1..0d6af99f348feadc1f257d880cd9899e88be7619 100644
--- a/ash/mus/window_manager_application.cc
+++ b/ash/mus/window_manager_application.cc
@@ -20,6 +20,7 @@
 #include "chromeos/network/network_connect.h"
 #include "chromeos/network/network_handler.h"
 #include "chromeos/system/fake_statistics_provider.h"
+#include "components/discardable_memory/client/client_discardable_shared_memory_manager.h"
 #include "device/bluetooth/bluetooth_adapter_factory.h"
 #include "device/bluetooth/dbus/bluez_dbus_manager.h"
 #include "services/service_manager/public/cpp/connection.h"
@@ -27,6 +28,7 @@
 #include "services/service_manager/public/cpp/service_context.h"
 #include "services/tracing/public/cpp/provider.h"
 #include "services/ui/common/accelerator_util.h"
+#include "services/ui/public/interfaces/constants.mojom.h"
 #include "ui/aura/env.h"
 #include "ui/aura/mus/window_tree_client.h"
 #include "ui/events/event.h"
@@ -107,17 +109,31 @@ void WindowManagerApplication::ShutdownComponents() {
 }
 
 void WindowManagerApplication::OnStart() {
+  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));
+  auto io_task_runner = io_thread_->task_runner();
   aura_init_ = base::MakeUnique<views::AuraInit>(
       context()->connector(), context()->identity(), "ash_mus_resources.pak",
-      "ash_mus_resources_200.pak", nullptr,
+      "ash_mus_resources_200.pak", io_task_runner,

[James Cook, 2017/03/09 21:00:21]

Can you add a comment somewhere (maybe in the AuraInit constructor) that
emphasizes that the IO task runner parameter really is for IPC and not for file
IO? At first I thought the task runner was related to loading the .pak files and
hence should be the FILE thread.

       views::AuraInit::Mode::AURA_MUS_WINDOW_MANAGER);
   window_manager_.reset(new WindowManager(context()->connector()));
 
+  discardable_memory::mojom::DiscardableSharedMemoryManagerPtr manager_ptr;

[James Cook, 2017/03/09 21:00:21]

This block of code seems like it should live down in //ui/views/mus. It seems
like discardable memory could be used by anyone who uses skia. AuraInit
sometimes constructs a MusClient and MusClient creates a discardable memory
allocator, so it seems like it should go down there.  WDYT?

[Peng, 2017/03/09 21:35:43]

+sky, for his opinion.

+  context()->connector()->BindInterface(ui::mojom::kServiceName, &manager_ptr);
+  discardable_shared_memory_manager_ = base::MakeUnique<
+      discardable_memory::ClientDiscardableSharedMemoryManager>(
+      std::move(manager_ptr), io_task_runner);
+  base::DiscardableMemoryAllocator::SetInstance(
+      discardable_shared_memory_manager_.get());
+
   tracing_.Initialize(context()->connector(), context()->identity().name());
 
   std::unique_ptr<aura::WindowTreeClient> window_tree_client =
       base::MakeUnique<aura::WindowTreeClient>(
-          context()->connector(), window_manager_.get(), window_manager_.get());
+          context()->connector(), window_manager_.get(), window_manager_.get(),
+          nullptr, io_task_runner);
   window_tree_client->ConnectAsWindowManager();
 
   const size_t kMaxNumberThreads = 3u;  // Matches that of content.