Introduce the RunService() method

The Service::Start() method is so long that its length negatively
affects readability of the code. Hence this patch that splits
Service::Start().

Test: Booted Android in Cuttlefish.
Change-Id: I5a6f587ecc5e6470137de6cceda7e685bce28ced
Signed-off-by: Bart Van Assche <bvanassche@google.com>
diff --git a/init/service.h b/init/service.h
index 54c923b..3f12aa2 100644
--- a/init/service.h
+++ b/init/service.h
@@ -147,6 +147,10 @@
     void ResetFlagsForStart();
     Result<void> CheckConsole();
     void ConfigureMemcg();
+    void RunService(
+            const std::optional<MountNamespace>& override_mount_namespace,
+            const std::vector<Descriptor>& descriptors,
+            std::unique_ptr<std::array<int, 2>, void (*)(const std::array<int, 2>* pipe)> pipefd);
 
     static unsigned long next_start_order_;
     static bool is_exec_service_running_;