Added a test to cover debugging step over.

tests/standalone/debugger/debug_lib.dart

 // Copyright (c) 2013, 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.
 
 // Library used by debugger wire protocol tests (standalone VM debugging).
 
 library DartDebugger;
 
 import "dart:async";
 import "dart:io";
@@ skipping 408 matching lines @@
     if (msg["event"] == "isolate") {
       if (msg["params"]["reason"] == "created") {
         isolateId = msg["params"]["id"];
         assert(isolateId != null);
         print("Debuggee isolate id $isolateId created.");
       } else if (msg["params"]["reason"] == "shutdown") {
         print("Debuggee isolate id ${msg["params"]["id"]} shut down.");
         shutdownEventSeen = true;
         if (!script.isEmpty) {
           error("Error: premature isolate shutdown event seen.");
+          error("Next expected event: ${script.currentEntry}");
         }
       }
     } else if (msg["event"] == "breakpointResolved") {
       var bpId = msg["params"]["breakpointId"];
       assert(bpId != null);
       var isolateId = msg["params"]["isolateId"];
       assert(isolateId != null);
       var location = msg["params"]["location"];
       assert(location != null);
       print("Isolate $isolateId: breakpoint $bpId resolved"
@@ skipping 174 matching lines @@
   targetOpts.add("--debuggee");
   print('args: ${targetOpts.join(" ")}');
 
   Process.start(Platform.executable, targetOpts).then((Process process) {
     print("Debug target process started, pid ${process.pid}.");
     process.stdin.close();
     var debugger = new Debugger(process, new DebugScript(script));
   });
   return true;
 }