Add flag —enable-debugger (default true) in order to disable debugger single stepping code.

runtime/vm/debugger.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 "vm/debugger.h"
 
 #include "include/dart_api.h"
 
 #include "vm/code_generator.h"
 #include "vm/code_patcher.h"
 #include "vm/compiler.h"
 #include "vm/dart_entry.h"
 #include "vm/deopt_instructions.h"
 #include "vm/flags.h"
 #include "vm/globals.h"
 #include "vm/longjump.h"
 #include "vm/json_stream.h"
 #include "vm/object.h"
 #include "vm/object_store.h"
 #include "vm/os.h"
 #include "vm/port.h"
 #include "vm/stack_frame.h"
 #include "vm/stub_code.h"
 #include "vm/symbols.h"
 #include "vm/visitor.h"
 
 
 namespace dart {
 
-DEFINE_FLAG(bool, verbose_debug, false, "Verbose debugger messages");
+DEFINE_FLAG(bool, enable_debugger, true, "Enables debugger step checks");
+DEFINE_FLAG(bool, show_invisible_frames, false,
+            "Show invisible frames in debugger stack traces");
 DEFINE_FLAG(bool, trace_debugger_stacktrace, false,
             "Trace debugger stacktrace collection");
-DEFINE_FLAG(bool, show_invisible_frames, false,
-            "Show invisible frames in debugger stack traces");
+DEFINE_FLAG(bool, verbose_debug, false, "Verbose debugger messages");
 
 
 Debugger::EventHandler* Debugger::event_handler_ = NULL;
 
 
 class RemoteObjectCache : public ZoneAllocated {
  public:
   explicit RemoteObjectCache(intptr_t initial_size);
   intptr_t AddObject(const Object& obj);
   RawObject* GetObj(intptr_t obj_id) const;
@@ skipping 2517 matching lines @@
 }
 
 
 void Debugger::RegisterCodeBreakpoint(CodeBreakpoint* bpt) {
   ASSERT(bpt->next() == NULL);
   bpt->set_next(code_breakpoints_);
   code_breakpoints_ = bpt;
 }
 
 }  // namespace dart