Switch root to /system in first stage mount

Bug: 79173823
Bug: 79758715
Test: boot hikey and observe that /system is the new root
Change-Id: I22f58f1332150ebae8e7e24eccfe780ff29eba7f
diff --git a/init/switch_root.h b/init/switch_root.h
new file mode 100644
index 0000000..d515e5d
--- /dev/null
+++ b/init/switch_root.h
@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 2018 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.
+ */
+
+#pragma once
+
+#include <string>
+
+namespace android {
+namespace init {
+
+void SwitchRoot(const std::string& new_root);
+
+}  // namespace init
+}  // namespace android