Change how debugger handles source breakpoints

tests/standalone/debugger/breakpoint_resolved_test.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.
 
 import "debug_lib.dart";
 
 main(List<String> arguments) {
   if (RunScript(testScript, arguments)) return;
 
   bar();
 
   print("Hello from debuggee");
 }
 
 bar() {
-
+  // Attempt to set breakpoint in this empty line does not
+  // result in a resolved breakpoint.
   print("bar");
 }
 
 var testScript = [
   MatchFrame(0, "main"),
   SetBreakpoint(10),
   SetBreakpoint(12),
   SetBreakpoint(16),
   Resume(),
   MatchFrame(0, "main"),
-  Resume(),
-  MatchFrame(0, "bar"),
-  Resume(),
+  Resume(),  // Next breakpoint expected in main, when bar() returns.
   MatchFrame(0, "main"),
+  // Only two breakpoint resolved events expected.
   ExpectEvent("breakpointResolved", {"breakpointId": 1}),
   ExpectEvent("breakpointResolved", {"breakpointId": 2}),
-  ExpectEvent("breakpointResolved", {"breakpointId": 3}),
   Resume(),
 ];