Rename Root to ArtifactRoot.

This is slightly more descriptive, and we will potentially want to use the name Root for a broader concept shared between ArtifactRoot and RootedPath.

PiperOrigin-RevId: 182082367
diff --git a/src/test/java/com/google/devtools/build/lib/skyframe/TreeArtifactBuildTest.java b/src/test/java/com/google/devtools/build/lib/skyframe/TreeArtifactBuildTest.java
index 3846003..1a9063b 100644
--- a/src/test/java/com/google/devtools/build/lib/skyframe/TreeArtifactBuildTest.java
+++ b/src/test/java/com/google/devtools/build/lib/skyframe/TreeArtifactBuildTest.java
@@ -40,8 +40,8 @@
 import com.google.devtools.build.lib.actions.Artifact.SpecialArtifact;
 import com.google.devtools.build.lib.actions.Artifact.SpecialArtifactType;
 import com.google.devtools.build.lib.actions.Artifact.TreeFileArtifact;
+import com.google.devtools.build.lib.actions.ArtifactRoot;
 import com.google.devtools.build.lib.actions.BuildFailedException;
-import com.google.devtools.build.lib.actions.Root;
 import com.google.devtools.build.lib.actions.cache.MetadataHandler;
 import com.google.devtools.build.lib.actions.util.ActionsTestUtil;
 import com.google.devtools.build.lib.actions.util.TestAction;
@@ -1183,7 +1183,7 @@
     Path path = execRoot.getRelative(execPath);
     return new SpecialArtifact(
         path,
-        Root.asDerivedRoot(execRoot, execRoot.getRelative("out")),
+        ArtifactRoot.asDerivedRoot(execRoot, execRoot.getRelative("out")),
         execPath,
         ACTION_LOOKUP_KEY,
         SpecialArtifactType.TREE);