Save compilation units in protobuf format.

Bug: 146224091
Test: manual
Change-Id: I7a856bab13f54c78efa0061421c3fcb9341bc6e7
diff --git a/android/config.go b/android/config.go
index 3c49c1a..1cb543d 100644
--- a/android/config.go
+++ b/android/config.go
@@ -835,6 +835,14 @@
 	return c.Getenv("XREF_CORPUS")
 }
 
+// Returns Compilation Unit encoding to use. Can be 'json' (default), 'proto' or 'all'.
+func (c *config) XrefCuEncoding() string {
+	if enc := c.Getenv("KYTHE_KZIP_ENCODING"); enc != "" {
+		return enc
+	}
+	return "json"
+}
+
 func (c *config) EmitXrefRules() bool {
 	return c.XrefCorpusName() != ""
 }