Support for recovery snapshot.

Bug: 171231437

Test: source build/envsetup.sh
Test: ALLOW_MISSING_DEPENDENCIES=true m -j nothing

Change-Id: I74636cf7f97e027a229a5ef7c776f2b7a42ead95
diff --git a/android/config.go b/android/config.go
index 89467d8..6ab798d 100644
--- a/android/config.go
+++ b/android/config.go
@@ -1053,6 +1053,10 @@
 	return String(c.config.productVariables.DeviceVndkVersion)
 }
 
+func (c *deviceConfig) RecoverySnapshotVersion() string {
+	return String(c.config.productVariables.RecoverySnapshotVersion)
+}
+
 func (c *deviceConfig) CurrentApiLevelForVendorModules() string {
 	return StringDefault(c.config.productVariables.DeviceCurrentApiLevelForVendorModules, "current")
 }
diff --git a/android/variable.go b/android/variable.go
index 753ddd7..4e9eef5e 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -181,6 +181,8 @@
 	DeviceCurrentApiLevelForVendorModules *string  `json:",omitempty"`
 	DeviceSystemSdkVersions               []string `json:",omitempty"`
 
+	RecoverySnapshotVersion *string `json:",omitempty"`
+
 	DeviceSecondaryArch        *string  `json:",omitempty"`
 	DeviceSecondaryArchVariant *string  `json:",omitempty"`
 	DeviceSecondaryCpuVariant  *string  `json:",omitempty"`