[Coverity] Fix uninitialized member, pass-by-val.

ppapi/native_client/src/trusted/plugin/pnacl_translate_thread.h

Index: ppapi/native_client/src/trusted/plugin/pnacl_translate_thread.h
diff --git a/ppapi/native_client/src/trusted/plugin/pnacl_translate_thread.h b/ppapi/native_client/src/trusted/plugin/pnacl_translate_thread.h
index 0ab5a423b3830689193e1f43b938069e245d274c..bbd5792c3157a57c070e1c01cc4f2753b74415cd 100644
--- a/ppapi/native_client/src/trusted/plugin/pnacl_translate_thread.h
+++ b/ppapi/native_client/src/trusted/plugin/pnacl_translate_thread.h
@@ -33,7 +33,7 @@ class PnaclTranslateThread {
   virtual ~PnaclTranslateThread();
   // TODO(jvoung/dschuff): handle surfaway issues when coordinator/plugin
   // goes away. This data may have to be refcounted not touched in that case.
-  void RunTranslate(pp::CompletionCallback finish_callback,
+  void RunTranslate(const pp::CompletionCallback& finish_callback,
                     const Manifest* manifest,
                     const Manifest* ld_manifest,
                     LocalTempFile* obj_file,