Expose build file label retrieval as a protected member.

PiperOrigin-RevId: 191752718
diff --git a/src/main/java/com/google/devtools/build/lib/query2/SkyQueryEnvironment.java b/src/main/java/com/google/devtools/build/lib/query2/SkyQueryEnvironment.java
index c96a9ec..0c8d656 100644
--- a/src/main/java/com/google/devtools/build/lib/query2/SkyQueryEnvironment.java
+++ b/src/main/java/com/google/devtools/build/lib/query2/SkyQueryEnvironment.java
@@ -760,19 +760,7 @@
 
           // Also add the BUILD file of the extension.
           if (buildFiles) {
-            Path buildFileForLoad = null;
-            try {
-              buildFileForLoad =
-                  pkgPath.getPackageBuildFile(loadTarget.getLabel().getPackageIdentifier());
-            } catch (NoSuchPackageException e) {
-              throw new QueryException(
-                  loadTarget.getLabel().getPackageIdentifier() + " does not exist in graph");
-            }
-            Label buildFileLabel =
-                Label.createUnvalidated(
-                    loadTarget.getLabel().getPackageIdentifier(),
-                    buildFileForLoad.getBaseName());
-
+            Label buildFileLabel = getBuildFileLabel(loadTarget.getLabel().getPackageIdentifier());
             addIfUniqueLabel(new FakeLoadTarget(buildFileLabel, pkg), seenLabels, dependentFiles);
           }
         }
@@ -781,6 +769,17 @@
     return dependentFiles;
   }
 
+  protected Label getBuildFileLabel(PackageIdentifier packageIdentifier) throws QueryException {
+    // TODO(bazel-team): Try avoid filesystem access here.
+    Path buildFileForLoad = null;
+    try {
+      buildFileForLoad = pkgPath.getPackageBuildFile(packageIdentifier);
+    } catch (NoSuchPackageException e) {
+      throw new QueryException(packageIdentifier + " does not exist in graph");
+    }
+    return Label.createUnvalidated(packageIdentifier, buildFileForLoad.getBaseName());
+  }
+
   private static void addIfUniqueLabel(Target node, Set<Label> labels, Set<Target> nodes) {
     if (labels.add(node.getLabel())) {
       nodes.add(node);