Linux: fix a bunch of NULL vs. 0 issues spotted by gcc 4.5.

chrome/browser/process_singleton_uitest.cc

 // Copyright (c) 2010 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.
 
 // This test validates that the ProcessSingleton class properly makes sure
 // that there is only one main browser process.
 //
 // It is currently compiled and run on Windows and Posix(non-Mac) platforms.
 // Mac uses system services and ProcessSingletonMac is a noop.  (Maybe it still
 // makes sense to test that the system services are giving the behavior we
@@ skipping 20 matching lines @@
 
 // This is for the code that is to be ran in multiple threads at once,
 // to stress a race condition on first process start.
 // We use the thread safe ref counted base class so that we can use the
 // NewRunnableMethod class to run the StartChrome methods in many threads.
 class ChromeStarter : public base::RefCountedThreadSafe<ChromeStarter> {
  public:
   explicit ChromeStarter(int timeout_ms, const FilePath& user_data_dir)
       : ready_event_(false /* manual */, false /* signaled */),
         done_event_(false /* manual */, false /* signaled */),
-        process_handle_(NULL),
+        process_handle_(base::kNullProcessHandle),
         process_terminated_(false),
         timeout_ms_(timeout_ms),
         user_data_dir_(user_data_dir) {
   }
 
   // We must reset some data members since we reuse the same ChromeStarter
   // object and start/stop it a few times. We must start fresh! :-)
   void Reset() {
     ready_event_.Reset();
     done_event_.Reset();
@@ skipping 265 matching lines @@
     pending_starters.empty();
     if (chrome_starters_[last_index]->process_handle_ !=
         base::kNullProcessHandle) {
       KillProcessTree(chrome_starters_[last_index]->process_handle_);
       chrome_starters_[last_index]->done_event_.Wait();
     }
   }
 }
 
 }  // namespace