Fix writing soong.variables .

ConfiguredJarList had a marshaler but no unmarshaler.

Bug: 182965747
Test: Presubmits.
Change-Id: Id03669f4a0a3d389063a4e4b11af6d6be63dbba3

android/config.go

@@ -19,6 +19,7 @@ package android
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io/ioutil"
 	"os"
@@ -1635,6 +1636,20 @@ func (l *ConfiguredJarList) UnmarshalJSON(b []byte) error {
 	return nil
 }
 
+func (l *ConfiguredJarList) MarshalJSON() ([]byte, error) {
+	if len(l.apexes) != len(l.jars) {
+		return nil, errors.New(fmt.Sprintf("Inconsistent ConfiguredJarList: apexes: %q, jars: %q", l.apexes, l.jars))
+	}
+
+	list := make([]string, 0, len(l.apexes))
+
+	for i := 0; i < len(l.apexes); i++ {
+		list = append(list, l.apexes[i]+":"+l.jars[i])
+	}
+
+	return json.Marshal(list)
+}
+
 // ModuleStem hardcodes the stem of framework-minus-apex to return "framework".
 //
 // TODO(b/139391334): hard coded until we find a good way to query the stem of a