Add the ability to set rlimits on the jailed process

Currently Chrome OS relies on upstart to configure these limits but
that isn't available when using libminijail from session manager.  Add
it so runtime limits can be configured for Android and other containers.

BUG=none
TEST=updated security_Minijail0 and manually check /proc/xxx/limits of
jailed process.

Change-Id: I62ed63c89c9c5196b7d9873520b396c9524e5855
Signed-off-by: Dylan Reid <dgreid@chromium.org>
diff --git a/libminijail.h b/libminijail.h
index 08fdf2b..bad8407 100644
--- a/libminijail.h
+++ b/libminijail.h
@@ -97,6 +97,9 @@
  */
 int minijail_use_alt_syscall(struct minijail *j, const char *table);
 
+/* Sets the given runtime limit. See getrlimit(2). */
+int minijail_rlimit(struct minijail *j, int type, uint32_t cur, uint32_t max);
+
 /*
  * Adds the jailed process to the cgroup given by |path|.  |path| should be the
  * full path to the cgroups "tasks" file.