init support for cgroups.

This adds the "writepid" option that instructs init to write the child's
pid to the given filenames (such as /dev/cpuctl/bg_non_interactive/cgroup.procs
and/or /dev/cpuset/foreground/cgroup.procs).

Bug: http://b/21163745
Change-Id: I121bb22aa208bc99c4fb334eb552fdd5bcc47c1a
diff --git a/init/init.h b/init/init.h
index 1cabb14..c166969 100644
--- a/init/init.h
+++ b/init/init.h
@@ -19,6 +19,9 @@
 
 #include <sys/types.h>
 
+#include <string>
+#include <vector>
+
 #include <cutils/list.h>
 #include <cutils/iosched_policy.h>
 
@@ -116,6 +119,8 @@
 
     struct action onrestart;  /* Actions to execute on restart. */
 
+    std::vector<std::string>* writepid_files_;
+
     /* keycodes for triggering this service via /dev/keychord */
     int *keycodes;
     int nkeycodes;