ozone: Initialize a subsystem only if necessary.

ui/gfx/ozone/surface_factory_ozone.cc

Index: ui/gfx/ozone/surface_factory_ozone.cc
diff --git a/ui/gfx/ozone/surface_factory_ozone.cc b/ui/gfx/ozone/surface_factory_ozone.cc
index f17c13dcf5a05f4293707480be90c36c8a45a1db..a1dbdd121dfd7cf284d9f372c1eac8eddfd3826c 100644
--- a/ui/gfx/ozone/surface_factory_ozone.cc
+++ b/ui/gfx/ozone/surface_factory_ozone.cc
@@ -16,9 +16,13 @@ namespace gfx {
 SurfaceFactoryOzone* SurfaceFactoryOzone::impl_ = NULL;
 
 SurfaceFactoryOzone::SurfaceFactoryOzone() {
+  CHECK(!impl_) << "There should only be a single SurfaceFactoryOzone.";
+  impl_ = this;
 }
 
 SurfaceFactoryOzone::~SurfaceFactoryOzone() {
+  CHECK_EQ(impl_, this);
+  impl_ = NULL;
 }
 
 SurfaceFactoryOzone* SurfaceFactoryOzone::GetInstance() {
@@ -26,10 +30,6 @@ SurfaceFactoryOzone* SurfaceFactoryOzone::GetInstance() {
   return impl_;
 }
 
-void SurfaceFactoryOzone::SetInstance(SurfaceFactoryOzone* impl) {
-  impl_ = impl;
-}
-
 intptr_t SurfaceFactoryOzone::GetNativeDisplay() {
   return 0;
 }