Update Fileset with the HasDigest interface.

RELNOTES: None
PiperOrigin-RevId: 257247094
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/TreeArtifactValue.java b/src/main/java/com/google/devtools/build/lib/skyframe/TreeArtifactValue.java
index 7b9407b..b51c1ae 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/TreeArtifactValue.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/TreeArtifactValue.java
@@ -22,6 +22,7 @@
 import com.google.common.collect.Maps;
 import com.google.devtools.build.lib.actions.Artifact.TreeFileArtifact;
 import com.google.devtools.build.lib.actions.FileArtifactValue;
+import com.google.devtools.build.lib.actions.HasDigest;
 import com.google.devtools.build.lib.actions.cache.DigestUtils;
 import com.google.devtools.build.lib.skyframe.serialization.autocodec.AutoCodec;
 import com.google.devtools.build.lib.util.BigIntegerFingerprint;
@@ -44,7 +45,7 @@
  * {@link TreeFileArtifact}s.
  */
 @AutoCodec
-public class TreeArtifactValue implements SkyValue {
+public class TreeArtifactValue implements HasDigest, SkyValue {
 
   private static final TreeArtifactValue EMPTY =
       new TreeArtifactValue(
@@ -106,7 +107,8 @@
   }
 
   @Nullable
-  byte[] getDigest() {
+  @Override
+  public byte[] getDigest() {
     return digest.clone();
   }
 
@@ -197,7 +199,7 @@
 
         @Nullable
         @Override
-        byte[] getDigest() {
+        public byte[] getDigest() {
           throw new UnsupportedOperationException();
         }