Revert "Revert "Include proguard flag files from transitive java_library deps""

This reverts commit 6f7e288fb5ea2fb01d9093fd57081a82c09a6618.

Reason for revert: Downstream proguard usage has been fixed.

Change-Id: I3667e7e908eebc62c640b42cb96b04993fc66e45
diff --git a/java/app.go b/java/app.go
index a822cbf..eb1b474 100755
--- a/java/app.go
+++ b/java/app.go
@@ -457,7 +457,7 @@
 func (a *AndroidApp) proguardBuildActions(ctx android.ModuleContext) {
 	var staticLibProguardFlagFiles android.Paths
 	ctx.VisitDirectDeps(func(m android.Module) {
-		if lib, ok := m.(AndroidLibraryDependency); ok && ctx.OtherModuleDependencyTag(m) == staticLibTag {
+		if lib, ok := m.(LibraryDependency); ok && ctx.OtherModuleDependencyTag(m) == staticLibTag {
 			staticLibProguardFlagFiles = append(staticLibProguardFlagFiles, lib.ExportedProguardFlagFiles()...)
 		}
 	})