Internal hook to extend JavaProtoAspect behavior.

PiperOrigin-RevId: 406364677
diff --git a/src/main/java/com/google/devtools/build/lib/rules/java/proto/JavaProtoAspect.java b/src/main/java/com/google/devtools/build/lib/rules/java/proto/JavaProtoAspect.java
index ebd890d..7db18a1 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/java/proto/JavaProtoAspect.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/java/proto/JavaProtoAspect.java
@@ -142,9 +142,18 @@
 
     rpcSupport.mutateAspectDefinition(result, aspectParameters);
 
+    mutateAspectDefinition(result, aspectParameters);
+
     return result.build();
   }
 
+  /**
+   * Invoked after the default aspect definition has been created. Override this to add further
+   * attributes, etc. Default implementation does nothing.
+   */
+  protected void mutateAspectDefinition(
+      AspectDefinition.Builder builder, AspectParameters aspectParameters) {}
+
   private static class Impl {
 
     private final RuleContext ruleContext;