Fix few trivial Coverity issues, mainly PASS_BY_VALUE.

base/simple_thread.h

 // Copyright (c) 2006-2008 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.
 
 // WARNING: You should probably be using Thread (thread.h) instead.  Thread is
 //          Chrome's message-loop based Thread abstraction, and if you are a
 //          thread running in the browser, there will likely be assumptions
 //          that your thread will have an associated message loop.
 //
 // This is a simple thread interface that backs to a native operating system
@@ skipping 134 matching lines @@
 // multi-threaded, but don't want to spawn a thread for each small bit of work.
 //
 // You just call AddWork() to add a delegate to the list of work to be done.
 // JoinAll() will make sure that all outstanding work is processed, and wait
 // for everything to finish.  You can reuse a pool, so you can call Start()
 // again after you've called JoinAll().
 class DelegateSimpleThreadPool : public DelegateSimpleThread::Delegate {
  public:
   typedef DelegateSimpleThread::Delegate Delegate;
 
-  DelegateSimpleThreadPool(const std::string name_prefix, int num_threads)
+  DelegateSimpleThreadPool(const std::string& name_prefix, int num_threads)
       : name_prefix_(name_prefix), num_threads_(num_threads),
         dry_(true, false) { }
   ~DelegateSimpleThreadPool();
 
   // Start up all of the underlying threads, and start processing work if we
   // have any.
   void Start();
 
   // Make sure all outstanding work is finished, and wait for and destroy all
   // of the underlying threads in the pool.
@@ skipping 14 matching lines @@
   int num_threads_;
   std::vector<DelegateSimpleThread*> threads_;
   std::queue<Delegate*> delegates_;
   Lock lock_;            // Locks delegates_
   WaitableEvent dry_;    // Not signaled when there is no work to do.
 };
 
 }  // namespace base
 
 #endif  // BASE_SIMPLE_THREAD_H_