Add an enum representing the specific build file name (WORKSPACE, BUILD) to the PackageLookupValue to reduce the number of references to the filename "BUILD".

--
MOS_MIGRATED_REVID=129203257
diff --git a/src/test/java/com/google/devtools/build/lib/skyframe/FileFunctionTest.java b/src/test/java/com/google/devtools/build/lib/skyframe/FileFunctionTest.java
index be33464..0269305 100644
--- a/src/test/java/com/google/devtools/build/lib/skyframe/FileFunctionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/skyframe/FileFunctionTest.java
@@ -65,12 +65,6 @@
 import com.google.devtools.build.skyframe.SkyFunctionName;
 import com.google.devtools.build.skyframe.SkyKey;
 import com.google.devtools.build.skyframe.SkyValue;
-
-import org.junit.Before;
-import org.junit.Test;
-import org.junit.runner.RunWith;
-import org.junit.runners.JUnit4;
-
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
@@ -85,8 +79,11 @@
 import java.util.UUID;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicReference;
-
 import javax.annotation.Nullable;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
 
 /** Tests for {@link FileFunction}. */
 @RunWith(JUnit4.class)