Add userspace_reboot.mk and include it in mainline_system.mk

The intention of userspace_reboot.mk is to provide a default
configuration (e.g. userspace reboot watchdog timeout) for devices that
are supporting userspace reboot feature. So far it only contains one
property that tells whenever device supports userspace reboot, more to
follow in separate CLs.

Test: flashed blueline, checked that property is set to true
Bug: 135984674
Change-Id: I32e6281ccc36236ec4fa5cde299753b6e0ece181

target/product/mainline_system.mk

@@ -24,6 +24,9 @@ $(call inherit-product-if-exists, vendor/google/security/adb/vendor_key.mk)
 # Enable updating of APEXes
 $(call inherit-product, $(SRC_TARGET_DIR)/product/updatable_apex.mk)
 
+# Mainline devices support userspace reboot
+$(call inherit-product, $(SRC_TARGET_DIR)/product/userspace_reboot.mk)
+
 # Shared java libs
 PRODUCT_PACKAGES += \
     com.android.nfc_extras \

target/product/userspace_reboot.mk

@@ -0,0 +1,21 @@
+#
+# Copyright (C) 2019 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.
+#
+
+# Inherit this when the target supports userspace reboot
+
+PRODUCT_PROPERTY_OVERRIDES := ro.init.userspace_reboot.is_supported=true
+
+# TODO(b/135984674): configure userspace reboot related properties