Rename MiddlemanExpander to ArtifactExpander, and refactor it to yield ArtifactFiles.

--
MOS_MIGRATED_REVID=114166208
diff --git a/src/test/java/com/google/devtools/build/lib/actions/ArtifactTest.java b/src/test/java/com/google/devtools/build/lib/actions/ArtifactTest.java
index cd97821..c0c992f 100644
--- a/src/test/java/com/google/devtools/build/lib/actions/ArtifactTest.java
+++ b/src/test/java/com/google/devtools/build/lib/actions/ArtifactTest.java
@@ -176,7 +176,7 @@
     List<String> paths = new ArrayList<>();
     MutableActionGraph actionGraph = new MapBasedActionGraph();
     Artifact.addExpandedExecPathStrings(getFooBarArtifacts(actionGraph, true), paths,
-        ActionInputHelper.actionGraphMiddlemanExpander(actionGraph));
+        ActionInputHelper.actionGraphArtifactExpander(actionGraph));
     assertThat(paths).containsExactly("bar1.h", "bar1.h", "bar2.h", "bar3.h");
   }
 
@@ -185,7 +185,7 @@
     List<PathFragment> paths = new ArrayList<>();
     MutableActionGraph actionGraph = new MapBasedActionGraph();
     Artifact.addExpandedExecPaths(getFooBarArtifacts(actionGraph, true), paths,
-        ActionInputHelper.actionGraphMiddlemanExpander(actionGraph));
+        ActionInputHelper.actionGraphArtifactExpander(actionGraph));
     assertThat(paths).containsExactly(
         new PathFragment("bar1.h"),
         new PathFragment("bar1.h"),
@@ -195,11 +195,11 @@
 
   @Test
   public void testAddExpandedArtifacts() throws Exception {
-    List<Artifact> expanded = new ArrayList<>();
+    List<ArtifactFile> expanded = new ArrayList<>();
     MutableActionGraph actionGraph = new MapBasedActionGraph();
     List<Artifact> original = getFooBarArtifacts(actionGraph, true);
     Artifact.addExpandedArtifacts(original, expanded,
-        ActionInputHelper.actionGraphMiddlemanExpander(actionGraph));
+        ActionInputHelper.actionGraphArtifactExpander(actionGraph));
 
     List<Artifact> manuallyExpanded = new ArrayList<>();
     for (Artifact artifact : original) {
@@ -226,7 +226,7 @@
     List<String> paths = new ArrayList<>();
     MutableActionGraph actionGraph = new MapBasedActionGraph();
     Artifact.addExpandedExecPathStrings(getFooBarArtifacts(actionGraph, true), paths,
-        ActionInputHelper.actionGraphMiddlemanExpander(actionGraph));
+        ActionInputHelper.actionGraphArtifactExpander(actionGraph));
     assertThat(paths).containsExactly("bar1.h", "bar1.h", "bar2.h", "bar3.h");
   }
 
@@ -235,7 +235,7 @@
     List<PathFragment> paths = new ArrayList<>();
     MutableActionGraph actionGraph = new MapBasedActionGraph();
     Artifact.addExpandedExecPaths(getFooBarArtifacts(actionGraph, true), paths,
-        ActionInputHelper.actionGraphMiddlemanExpander(actionGraph));
+        ActionInputHelper.actionGraphArtifactExpander(actionGraph));
     assertThat(paths).containsExactly(
         new PathFragment("bar1.h"),
         new PathFragment("bar1.h"),
@@ -243,13 +243,14 @@
         new PathFragment("bar3.h"));
   }
 
+  // TODO consider tests for the future
   @Test
   public void testAddExpandedArtifactsNewActionGraph() throws Exception {
-    List<Artifact> expanded = new ArrayList<>();
+    List<ArtifactFile> expanded = new ArrayList<>();
     MutableActionGraph actionGraph = new MapBasedActionGraph();
     List<Artifact> original = getFooBarArtifacts(actionGraph, true);
     Artifact.addExpandedArtifacts(original, expanded,
-        ActionInputHelper.actionGraphMiddlemanExpander(actionGraph));
+        ActionInputHelper.actionGraphArtifactExpander(actionGraph));
 
     List<Artifact> manuallyExpanded = new ArrayList<>();
     for (Artifact artifact : original) {