Change the key type we keep around in our fileset mappings.

There is no need to throw away the fact that the mapping is artifact -> fileset symlinks so early.

This CL is otherwise a no-op.

RELNOTES: None
PiperOrigin-RevId: 211808154
diff --git a/src/main/java/com/google/devtools/build/lib/actions/BaseSpawn.java b/src/main/java/com/google/devtools/build/lib/actions/BaseSpawn.java
index aa49f2f..dcba403 100644
--- a/src/main/java/com/google/devtools/build/lib/actions/BaseSpawn.java
+++ b/src/main/java/com/google/devtools/build/lib/actions/BaseSpawn.java
@@ -88,7 +88,7 @@
   }
 
   @Override
-  public ImmutableMap<PathFragment, ImmutableList<FilesetOutputSymlink>> getFilesetMappings() {
+  public ImmutableMap<Artifact, ImmutableList<FilesetOutputSymlink>> getFilesetMappings() {
     return ImmutableMap.of();
   }