Clean VM thread shutdown:

runtime/vm/debugger_api_impl_test.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "include/dart_mirrors_api.h"
 #include "include/dart_tools_api.h"
 #include "platform/assert.h"
 #include "vm/dart_api_impl.h"
 #include "vm/lockers.h"
 #include "vm/unit_test.h"
@@ skipping 1387 matching lines @@
   ASSERT(isolate != NULL);
   Dart_EnterScope();
   LoadScript(kScriptChars);
   Dart_Handle retval = Invoke("main");
   EXPECT_VALID(retval);
   EXPECT(test_isolate_id != ILLEGAL_ISOLATE_ID);
   EXPECT(Dart_GetIsolate(test_isolate_id) == isolate);
   EXPECT(Dart_GetIsolateId(isolate) == test_isolate_id);
   Dart_ExitScope();
   Dart_ShutdownIsolate();
+  Dart_SetIsolateEventHandler(NULL);
   EXPECT(verify_callback == 0x5);  // Only created and shutdown events.
 }
 
 
 static Monitor* sync = NULL;
 static bool isolate_interrupted = false;
 static bool pause_event_handled = false;
 static Dart_IsolateId interrupt_isolate_id = ILLEGAL_ISOLATE_ID;
 static volatile bool continue_isolate_loop = true;
 
@@ skipping 895 matching lines @@
       " null, 3, 7, 1, 8, 6, 9, 10, 10, 11, 11, 13,"
       " null, 4, 13, 3, 14, 10,"
       " null, 5, 17, 5, 18, 9, 19, 12,"
       " null, 6, 21, 1,"
       " null, 8, 24, 1, 25, 5, 26, 6, 27, 8,"
       " null, 9, 29, 1]",
       tokens_cstr);
 }
 
 }  // namespace dart