Add support for sandboxing persistent workers.

--
MOS_MIGRATED_REVID=134523222
diff --git a/src/main/java/com/google/devtools/build/lib/sandbox/SandboxHelpers.java b/src/main/java/com/google/devtools/build/lib/sandbox/SandboxHelpers.java
index de018b1..8ab9762 100644
--- a/src/main/java/com/google/devtools/build/lib/sandbox/SandboxHelpers.java
+++ b/src/main/java/com/google/devtools/build/lib/sandbox/SandboxHelpers.java
@@ -38,7 +38,7 @@
 import java.util.concurrent.atomic.AtomicInteger;
 
 /** Helper methods that are shared by the different sandboxing strategies in this package. */
-final class SandboxHelpers {
+public final class SandboxHelpers {
 
   static void lazyCleanup(
       ExecutorService backgroundWorkers,
@@ -84,7 +84,7 @@
     }
   }
 
-  static ImmutableSet<PathFragment> getOutputFiles(Spawn spawn) {
+  public static ImmutableSet<PathFragment> getOutputFiles(Spawn spawn) {
     Builder<PathFragment> outputFiles = ImmutableSet.builder();
     for (PathFragment optionalOutput : spawn.getOptionalOutputFiles()) {
       Preconditions.checkArgument(!optionalOutput.isAbsolute());