Fix some typos in ART.

Test: m build-art-host
Test: m cpplint-art
Change-Id: Ifc6ce3d0d645c4a8dca72dd483fc03fc05077130
diff --git a/runtime/gc/reference_processor.h b/runtime/gc/reference_processor.h
index b15544d..38b68cb 100644
--- a/runtime/gc/reference_processor.h
+++ b/runtime/gc/reference_processor.h
@@ -42,7 +42,7 @@
 
 class Heap;
 
-// Used to process java.lang.References concurrently or paused.
+// Used to process java.lang.ref.Reference instances concurrently or paused.
 class ReferenceProcessor {
  public:
   explicit ReferenceProcessor();