Move the remaning files in content\common to the content namespace.

content/common/npobject_base.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.
 //
 // Base interface used by NPChannelBase and implemented by NPObjectProxy and
 // NPObjectStub.
 
 #ifndef CONTENT_COMMON_NPOBJECT_BASE_H_
 #define CONTENT_COMMON_NPOBJECT_BASE_H_
 
 #include "ipc/ipc_listener.h"
 #include "third_party/npapi/bindings/npruntime.h"
 
 struct NPObject;
 
+namespace content {
+
 class NPObjectBase {
  public:
   virtual ~NPObjectBase() {}
 
   // Returns the underlying NPObject handled by this NPObjectBase instance.
   virtual NPObject* GetUnderlyingNPObject() = 0;
 
   // Returns the channel listener for this NPObjectBase instance.
   virtual IPC::Listener* GetChannelListener() = 0;
 };
 
+}  // namespace content
+
 #endif  // CONTENT_COMMON_NPOBJECT_BASE_H_