services/ui: Have an explicit lifetime/ownership of ui::GpuService.

services/ui/common/gpu_service.cc

Index: services/ui/common/gpu_service.cc
diff --git a/services/ui/common/gpu_service.cc b/services/ui/common/gpu_service.cc
index f8bf9e79e0939d11ced35b5e1313616fe85c0011..9a2f4c561a3e4b28576250d2b1782b026dcdc69e 100644
--- a/services/ui/common/gpu_service.cc
+++ b/services/ui/common/gpu_service.cc
@@ -47,21 +47,18 @@ GpuService::GpuService(shell::Connector* connector)
 
 GpuService::~GpuService() {
   DCHECK(IsMainThread());
+  DCHECK_EQ(this, g_gpu_service);
   if (gpu_channel_)
     gpu_channel_->DestroyChannel();
+  g_gpu_service = nullptr;
 }
 
 // static
-void GpuService::Initialize(shell::Connector* connector) {
+std::unique_ptr<GpuService> GpuService::Initialize(
+    shell::Connector* connector) {
   DCHECK(!g_gpu_service);
   g_gpu_service = new GpuService(connector);
-}
-
-// static
-void GpuService::Terminate() {
-  DCHECK(g_gpu_service);
-  delete g_gpu_service;
-  g_gpu_service = nullptr;
+  return base::WrapUnique(g_gpu_service);
 }
 
 // static