services/ui: Allow injecting the IO thread task runner for gpu channel.

ui/views/mus/window_manager_connection.cc

Index: ui/views/mus/window_manager_connection.cc
diff --git a/ui/views/mus/window_manager_connection.cc b/ui/views/mus/window_manager_connection.cc
index ef2f6eb5d490b098c39efb6c4a1b76f84a3047a8..bfa45230e7d99218d36a55163e4bba8e5a59c273 100644
--- a/ui/views/mus/window_manager_connection.cc
+++ b/ui/views/mus/window_manager_connection.cc
@@ -58,10 +58,11 @@ WindowManagerConnection::~WindowManagerConnection() {
 // static
 std::unique_ptr<WindowManagerConnection> WindowManagerConnection::Create(
     shell::Connector* connector,
-    const shell::Identity& identity) {
+    const shell::Identity& identity,
+    scoped_refptr<base::SingleThreadTaskRunner> task_runner) {
   DCHECK(!lazy_tls_ptr.Pointer()->Get());
   WindowManagerConnection* connection =
-      new WindowManagerConnection(connector, identity);
+      new WindowManagerConnection(connector, identity, std::move(task_runner));
   DCHECK(lazy_tls_ptr.Pointer()->Get());
   return base::WrapUnique(connection);
 }
@@ -106,11 +107,12 @@ const std::set<ui::Window*>& WindowManagerConnection::GetRoots() const {
 
 WindowManagerConnection::WindowManagerConnection(
     shell::Connector* connector,
-    const shell::Identity& identity)
+    const shell::Identity& identity,
+    scoped_refptr<base::SingleThreadTaskRunner> task_runner)
     : connector_(connector), identity_(identity) {
   lazy_tls_ptr.Pointer()->Set(this);
 
-  gpu_service_ = ui::GpuService::Initialize(connector);
+  gpu_service_ = ui::GpuService::Create(connector, std::move(task_runner));
   compositor_context_factory_.reset(
       new views::SurfaceContextFactory(gpu_service_.get()));
   aura::Env::GetInstance()->set_context_factory(