Removed the debug message thread.

Removed the debug message thread.

The debug message thread was introduced to make it possible to have the message handler callback be called from a different thread than the thread running V8 where the debug event occoured, but it never had any practical use, and prevents providing information to the message handler which is only available from the V8 thread.

In the future any thread decoupling will have do be done by the embedder.

This also removes the queue used for outbound messages.

Renamed the class Message to CommandMessage as it is only used for debugger commands from the client. Related message queue classes has also been renamed.
Review URL: http://codereview.chromium.org/93118

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1788 ce2b1a6d-e550-0410-aec6-3dcde31c8c00