Use the event-handler for timers.

tests/debugger/async_expected.txt

Index: tests/debugger/async_expected.txt
diff --git a/tests/debugger/async_expected.txt b/tests/debugger/async_expected.txt
index 2350424f6db366ef722506f47558b68b3310fe35..0ab7d340ee55029ab544de6b54eb6ec5cdfb48d3 100644
--- a/tests/debugger/async_expected.txt
+++ b/tests/debugger/async_expected.txt
@@ -4,16 +4,16 @@ Starting session. Type 'help' for a list of commands.
 breakpoint set: id: '0' method: 'breakHere' bytecode index: '0'
 > r
 Stack trace:
-> 0: breakHere                	@void breakHere(){}
+> 0: breakHere                     	@void breakHere(){}
 > t internal
 Stack trace:
-> 0: breakHere                	@void breakHere(){}
-  1: call                     	
-  2: Future.call              	@computation()
-  3: _handleEvents            	@event()
-  4: call                     	
-  5: runToEnd                 	@entry()
-  6: Fiber.call               	@fletch.runToEnd(entry)
-  7: Coroutine._coroutineStart	@entry(argument)
+> 0: breakHere                     	@void breakHere(){}
+  1: call                          	
+  2: Future.call                   	@computation()
+  3: Object._noSuchMethodTrampoline	
+  4: _FletchTimer.call             	@_callback()
+  5: runToEnd                      	@entry()
+  6: Fiber.call                    	@fletch.runToEnd(entry)
+  7: Coroutine._coroutineStart     	@entry(argument)
 > c
 ### process terminated