Take Module implementations out of java/java.go.

Test: TreeHugger
Change-Id: I5c39915ad2cadf5981c201a2b412916524d4c3e2
diff --git a/java/gen.go b/java/gen.go
index 4f928d5..445a2d8 100644
--- a/java/gen.go
+++ b/java/gen.go
@@ -174,6 +174,12 @@
 	logtags() android.Paths
 }
 
+func (j *Module) logtags() android.Paths {
+	return j.logtagsSrcs
+}
+
+var _ logtagsProducer = (*Module)(nil)
+
 type logtagsSingleton struct{}
 
 func (l *logtagsSingleton) GenerateBuildActions(ctx android.SingletonContext) {