Scaffolding for overriding DirectoryListingStateFunction.

RELNOTES: None.
PiperOrigin-RevId: 218438432

src/main/java/com/google/devtools/build/lib/skyframe/SkyframeExecutor.java

diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeExecutor.java b/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeExecutor.java
index b3e7a67..aa36349 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeExecutor.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeExecutor.java
@@ -434,8 +434,7 @@
     map.put(SkyFunctions.CLIENT_ENVIRONMENT_VARIABLE, new ClientEnvironmentFunction(clientEnv));
     map.put(SkyFunctions.ACTION_ENVIRONMENT_VARIABLE, new ActionEnvironmentFunction());
     map.put(FileStateValue.FILE_STATE, newFileStateFunction());
-    map.put(SkyFunctions.DIRECTORY_LISTING_STATE,
-        new DirectoryListingStateFunction(externalFilesHelper));
+    map.put(SkyFunctions.DIRECTORY_LISTING_STATE, newDirectoryListingStateFunction());
     map.put(SkyFunctions.FILE_SYMLINK_CYCLE_UNIQUENESS,
         new FileSymlinkCycleUniquenessFunction());
     map.put(SkyFunctions.FILE_SYMLINK_INFINITE_EXPANSION_UNIQUENESS,
@@ -582,6 +581,10 @@
     return new FileStateFunction(tsgm, externalFilesHelper);
   }
 
+  protected SkyFunction newDirectoryListingStateFunction() {
+    return new DirectoryListingStateFunction(externalFilesHelper);
+  }
+
   protected SkyFunction newGlobFunction() {
     return new GlobFunction(/*alwaysUseDirListing=*/false);
   }