A new debugger.

Lots of bugs/rough edges/etc - issues will be filed.
Old-style debugging still works (just use --emit_source_annotations to get
the helpful movs back and --break_on_instruction will still fire).

src/xenia/ui/loop.h

@@ -31,6 +31,9 @@ class Loop {
   Loop();
   virtual ~Loop();
 
+  // Returns true if the currently executing code is within the loop thread.
+  virtual bool is_on_loop_thread() = 0;
+
   virtual void Post(std::function<void()> fn) = 0;
   virtual void PostDelayed(std::function<void()> fn, uint64_t delay_millis) = 0;
   void PostSynchronous(std::function<void()> fn);