Introduce enum to quickly discriminate AST nodes.

RELNOTES: None.
PiperOrigin-RevId: 166370036
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/FuncallExpression.java b/src/main/java/com/google/devtools/build/lib/syntax/FuncallExpression.java
index e034b16..f3019e4 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/FuncallExpression.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/FuncallExpression.java
@@ -761,6 +761,11 @@
   }
 
   @Override
+  public Kind kind() {
+    return Kind.FUNCALL;
+  }
+
+  @Override
   protected boolean isNewScope() {
     return true;
   }