In preparation for becoming an internal plugin in chrome I did these things:...

plugin/mac/plugin_mac.h

 /*
  * Copyright 2009, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 23 matching lines @@
 #define O3D_PLUGIN_MAC_PLUGIN_MAC_H_
 
 #include <CoreFoundation/CoreFoundation.h>
 #include <npupp.h>
 #include <AGL/agl.h>
 #include <vector>
 
 // Just for o3d::Event::Button at the moment.
 #include "core/cross/event.h"
 
+namespace o3d {
 
 // RenderTimer maintains an animation timer (nominally running at 60fps)
 //
 // Keeps track of the current NPP instances running in the browser and then
 // renders each one during each timer callback.
 class RenderTimer {
  public:
   RenderTimer() {}
 
   void Start();
@@ skipping 40 matching lines @@
 bool HandleMacEvent(EventRecord* the_event, NPP instance);
 
 o3d::Event::Button MacOSMouseButtonNumberToO3DButton(int inButton);
 
 bool GetBrowserVersionInfo(int *returned_major,
                            int *returned_minor,
                            int *returned_bugfix);
 
 bool UseSoftwareRenderer();
 
+}  // namespace o3d
+
 #endif  // O3D_PLUGIN_MAC_PLUGIN_MAC_H_