Fix various linter errors

RELNOTES: None.
PiperOrigin-RevId: 170418147
diff --git a/src/test/java/com/google/devtools/build/lib/skyframe/TimestampBuilderTestCase.java b/src/test/java/com/google/devtools/build/lib/skyframe/TimestampBuilderTestCase.java
index 15d0b04..d39d857 100644
--- a/src/test/java/com/google/devtools/build/lib/skyframe/TimestampBuilderTestCase.java
+++ b/src/test/java/com/google/devtools/build/lib/skyframe/TimestampBuilderTestCase.java
@@ -422,6 +422,7 @@
     }
   }
 
+  /** In-memory {@link ActionCache} backed by a HashMap */
   protected static class InMemoryActionCache implements ActionCache {
 
     private final Map<String, Entry> actionCache = new HashMap<>();