Add virtual A/B product.

- Add PRODUCT_VIRTUAL_AB_OTA(_RETROFIT)
- Set ro.virtual_ab.{enabled,retrofit} respectively.

A device will do the following to enable virtual a/b or retrofit:

$(call inherit-product, $(SRC_TARGET_DIR)/product/virtual_ab_ota.mk)
$(call inherit-product, $(SRC_TARGET_DIR)/product/virtual_ab_ota_retrofit.mk)

Bug: 135752105
Test: build with device with flag set
Change-Id: I6cb1207aef3ddcc40e215e20589abf995ec81aac

core/product.mk

@@ -368,6 +368,12 @@ _product_list_vars += PRODUCT_UPDATABLE_BOOT_LOCATIONS
 # Whether the product would like to check prebuilt ELF files.
 _product_single_value_vars += PRODUCT_CHECK_ELF_FILES
 
+# If set, device uses virtual A/B.
+_product_single_value_vars += PRODUCT_VIRTUAL_AB_OTA
+
+# If set, device retrofits virtual A/B.
+_product_single_value_vars += PRODUCT_VIRTUAL_AB_OTA_RETROFIT
+
 .KATI_READONLY := _product_single_value_vars _product_list_vars
 _product_var_list :=$= $(_product_single_value_vars) $(_product_list_vars)
 

target/product/virtual_ab_ota.mk

@@ -0,0 +1,19 @@
+#
+# 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.
+#
+
+PRODUCT_VIRTUAL_AB_OTA := true
+
+PRODUCT_PRODUCT_PROPERTIES += ro.virtual_ab.enabled=true

target/product/virtual_ab_ota_retrofit.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.
+#
+
+$(call inherit-product, $(SRC_TARGET_DIR)/product/virtual_ab_ota.mk)
+
+PRODUCT_VIRTUAL_AB_OTA_RETROFIT := true
+
+PRODUCT_PRODUCT_PROPERTIES += ro.virtual_ab.retrofit=true