Add support for dumping proguard api file.

Test: ref go/ag/4783442
Bug: b/70351683
Change-Id: I0aedd41686535c9a662b935003b80634e56663e0
Merged-In: I0aedd41686535c9a662b935003b80634e56663e0
(cherry-picked from commit: 26c055258b92b8c5ba428cd6c1c6bd7e6c457d49)
diff --git a/java/androidmk.go b/java/androidmk.go
index aebbcc8..877d840 100644
--- a/java/androidmk.go
+++ b/java/androidmk.go
@@ -379,6 +379,9 @@
 				if ddoc.exactApiFile != nil {
 					fmt.Fprintln(w, apiFilePrefix+"EXACT_API_FILE := ", ddoc.exactApiFile.String())
 				}
+				if ddoc.proguardFile != nil {
+					fmt.Fprintln(w, apiFilePrefix+"PROGUARD_FILE := ", ddoc.proguardFile.String())
+				}
 			},
 		},
 	}