Debugger message handler can be called from V8 thread.

Debugger message handler can be called from V8 thread.

The message handler function set through the debugger API is normally called in a different thread than the V8 thread where execution is stopped due to debugger event. This change adds an option to the API for specifying that the message handler should be called directly from the V8 thread. For an application like Chrome where thread dispatching is already in place this makes more sense.

Add an option to the message handler debugger API to process messages in the thread where V8 is running instead of posting it to a queue for processing on a additional thread.
Review URL: http://codereview.chromium.org/42643

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1627 ce2b1a6d-e550-0410-aec6-3dcde31c8c00