FilteredRepository: Implement abstract getIdentifier() method

Change-Id: I8a60c987dac205335a24c1d2dcf8a93608d6cf0c
diff --git a/src/main/java/com/googlesource/gerrit/plugins/gitiles/FilteredRepository.java b/src/main/java/com/googlesource/gerrit/plugins/gitiles/FilteredRepository.java
index 3c65e9e..2029595 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/gitiles/FilteredRepository.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/gitiles/FilteredRepository.java
@@ -139,6 +139,11 @@
   }
 
   @Override
+  public String getIdentifier() {
+    return delegate.getIdentifier();
+  }
+
+  @Override
   public void scanForRepoChanges() throws IOException {
     throw new UnsupportedOperationException(); // Gitiles is read-only.
   }