Pass large object by const ref

ppapi/thunk/enter.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PPAPI_THUNK_ENTER_H_
 #define PPAPI_THUNK_ENTER_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 185 matching lines @@
 
 // ----------------------------------------------------------------------------
 
 // Like EnterResource but assumes the lock is already held.
 template<typename ResourceT>
 class EnterResourceNoLock : public EnterResource<ResourceT, false> {
  public:
   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) {
   }
 };
 
 // EnterInstance ---------------------------------------------------------------
 
 class PPAPI_THUNK_EXPORT EnterInstance
     : public subtle::EnterBase,
       public subtle::LockOnEntry<true> {
@@ skipping 52 matching lines @@
   ResourceCreationAPI* functions() { return functions_; }
 
  private:
   ResourceCreationAPI* functions_;
 };
 
 }  // namespace thunk
 }  // namespace ppapi
 
 #endif  // PPAPI_THUNK_ENTER_H_