init: support setting rlimits per service

Add a new service option, `rlimit` that allows a given rlimit to be
set for a specific service instead of globally.

Use the same parsing, now allowing text such as 'cpu' or 'rtprio'
instead of relying on the enum value for the `setrlimit` builtin
command as well.

Bug: 63882119
Bug: 64894637

Test: boot bullhead, run a test app that attempts to set its rtprio to
      95, see that the priority set fails normally but passes when
      `rlimit rtprio 99 99` is used as its service option.
      See that this fails when `rlimit rtprio 50 50` is used as well.
Test: new unit tests

Change-Id: I4a13ca20e8529937d8b4bc11718ffaaf77523a52
diff --git a/init/rlimit_parser.h b/init/rlimit_parser.h
new file mode 100644
index 0000000..0396463
--- /dev/null
+++ b/init/rlimit_parser.h
@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _INIT_RLIMIT_PARSER_H
+#define _INIT_RLIMIT_PARSER_H
+
+#include <sys/resource.h>
+
+#include <string>
+#include <vector>
+
+#include "result.h"
+
+namespace android {
+namespace init {
+
+Result<std::pair<int, rlimit>> ParseRlimit(const std::vector<std::string>& args);
+
+}  // namespace init
+}  // namespace android
+
+#endif