Pass along the QueryExpressionContext from SkyQueryEnvironment#getRBuildFiles
to RBuildFilesVisitor#processPartialResults and back to
SkyQueryEnvironment#getBuildFileTargetsForPackageKeysAndProcessViaCallback.

Also improve a few comments.

RELNOTES: None
PiperOrigin-RevId: 214981215
diff --git a/src/main/java/com/google/devtools/build/lib/query2/ParallelSkyQueryUtils.java b/src/main/java/com/google/devtools/build/lib/query2/ParallelSkyQueryUtils.java
index 030ec3e..f8d6a3a 100644
--- a/src/main/java/com/google/devtools/build/lib/query2/ParallelSkyQueryUtils.java
+++ b/src/main/java/com/google/devtools/build/lib/query2/ParallelSkyQueryUtils.java
@@ -164,10 +164,11 @@
   static void getRBuildFilesParallel(
       SkyQueryEnvironment env,
       Collection<PathFragment> fileIdentifiers,
+      QueryExpressionContext<Target> context,
       Callback<Target> callback) throws QueryException, InterruptedException {
     Uniquifier<SkyKey> keyUniquifier = env.createSkyKeyUniquifier();
     RBuildFilesVisitor visitor =
-        new RBuildFilesVisitor(env, keyUniquifier, callback);
+        new RBuildFilesVisitor(env, keyUniquifier, context, callback);
     visitor.visitAndWaitForCompletion(env.getFileStateKeysForFileFragments(fileIdentifiers));
   }