Cycles: Report system memory usage and peak after scene device update

This only happens when built with WITH_CYCLES_DEBUG flag, memory statistics
is coming from guarded STL allocator.

intern/cycles/render/scene.cpp

@@ -36,6 +36,11 @@
 #include "util_foreach.h"
 #include "util_progress.h"
 
+#ifdef WITH_CYCLES_DEBUG
+#  include "util_guarded_allocator.h"
+#  include "util_logging.h"
+#endif
+
 CCL_NAMESPACE_BEGIN
 
 Scene::Scene(const SceneParams& params_, const DeviceInfo& device_info_)
@@ -239,6 +244,12 @@ void Scene::device_update(Device *device_, Progress& progress)
 		progress.set_status("Updating Device", "Writing constant memory");
 		device->const_copy_to("__data", &dscene.data, sizeof(dscene.data));
 	}
+
+#ifdef WITH_CYCLES_DEBUG
+	VLOG(1) << "System memory statistics after full device sync:\n"
+	        << "  Usage: " << util_guarded_get_mem_used() << "\n"
+	        << "  Peak: " << util_guarded_get_mem_peak();
+#endif
 }
 
 Scene::MotionType Scene::need_motion(bool advanced_shading)