Insert debug step check at the beginning of a function.

tests/standalone/debugger/break_at_equals_test.dart

 // Copyright (c) 2014, 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";
 
 class MyClass {
   operator ==(other) {
     print(other);
     return true;  // Breakpoint #3.
@@ skipping 15 matching lines @@
     throw "unreachable";
   }
   print("ok");
 }
 
 // Checks that debugger can stop at calls to == even if one
 // of the operands is null.
 
 var testScript = [
   MatchFrames(["main"]),
-  MatchLine(15),
+  MatchLine(14),
   SetBreakpoint(18),
   SetBreakpoint(21),
   SetBreakpoint(10),
   SetBreakpoint(23),
   Resume(),
   MatchFrames(["main"]),
   MatchLine(18),  // At breakpoint #1.
   Resume(),
   MatchLine(21),  // At breakpoint #2; didn't hit breakpoint in MyClass.==.
   Resume(),
   MatchFrames(["MyClass.==", "main"]),
   MatchLine(10),  // At breakpoint #3 in MyClass.==.
   Resume(),
   MatchLine(23),  // At breakpoint #4.
   Resume()
 ];