Start automatically generating operator<<s for enums.

Change-Id: I0f53db089b9a1ba38ce82b75ab22448877be67e0
diff --git a/src/indirect_reference_table.h b/src/indirect_reference_table.h
index b1f6d8c..b0a0d64 100644
--- a/src/indirect_reference_table.h
+++ b/src/indirect_reference_table.h
@@ -106,12 +106,12 @@
  * For convenience these match up with enum jobjectRefType from jni.h.
  */
 enum IndirectRefKind {
-    kSirtOrInvalid = 0,
-    kLocal         = 1,
-    kGlobal        = 2,
-    kWeakGlobal    = 3
+  kSirtOrInvalid = 0, // <<stack indirect reference table or invalid reference>>
+  kLocal         = 1, // <<local reference>>
+  kGlobal        = 2, // <<global reference>>
+  kWeakGlobal    = 3  // <<weak global reference>>
 };
-std::ostream& operator<<(std::ostream& os, IndirectRefKind rhs);
+std::ostream& operator<<(std::ostream& os, const IndirectRefKind& rhs);
 
 /*
  * Determine what kind of indirect reference this is.