Pass large object by const ref

ppapi/thunk/enter.h

Index: ppapi/thunk/enter.h
diff --git a/ppapi/thunk/enter.h b/ppapi/thunk/enter.h
index 098a2a81351eba2080dfe66007f3c267e96885e4..276f0457647d07d08f367cbced88430fdf781c3c 100644
--- a/ppapi/thunk/enter.h
+++ b/ppapi/thunk/enter.h
@@ -203,7 +203,8 @@ class EnterResourceNoLock : public EnterResource<ResourceT, false> {
   EnterResourceNoLock(PP_Resource resource, bool report_error)
       : EnterResource<ResourceT, false>(resource, report_error) {
   }
-  EnterResourceNoLock(PP_Resource resource, PP_CompletionCallback callback,
+  EnterResourceNoLock(PP_Resource resource,
+                      const PP_CompletionCallback& callback,
                       bool report_error)
       : EnterResource<ResourceT, false>(resource, callback, report_error) {
   }