Implement directed recovery snapshot.

Bug: 177451657
Test: m -j nothing
Change-Id: I0b84c34fb2e9e9340d9f9e7405428cd2cc4d43b5
diff --git a/android/variable.go b/android/variable.go
index 799369d..e76d683 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -307,6 +307,9 @@
 	DirectedVendorSnapshot bool            `json:",omitempty"`
 	VendorSnapshotModules  map[string]bool `json:",omitempty"`
 
+	DirectedRecoverySnapshot bool            `json:",omitempty"`
+	RecoverySnapshotModules  map[string]bool `json:",omitempty"`
+
 	BoardVendorSepolicyDirs      []string `json:",omitempty"`
 	BoardOdmSepolicyDirs         []string `json:",omitempty"`
 	BoardReqdMaskPolicy          []string `json:",omitempty"`