Add a check to JSON code

runtime/vm/debugger_api_impl.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_debugger_api.h"
 
 #include "vm/dart_api_impl.h"
 #include "vm/dart_api_state.h"
 #include "vm/debugger.h"
 #include "vm/isolate.h"
@@ skipping 69 matching lines @@
   BreakpointHandler* handler =
       reinterpret_cast<BreakpointHandler*>(bp_handler);
 
   isolate->debugger()->SetBreakpointHandler(handler);
 }
 
 
 static Dart_BreakpointResolvedHandler* bp_resolved_handler = NULL;
 
 static void DebuggerEventHandler(Debugger::DebuggerEvent* event) {
-  printf("Debugger event %d\n", event->type);
   Isolate* isolate = Isolate::Current();
   ASSERT(isolate != NULL);
   if (event->type == Debugger::kBreakpointResolved) {
     if (bp_resolved_handler == NULL) {
       return;
     }
     SourceBreakpoint* bpt = event->breakpoint;
     ASSERT(bpt != NULL);
     Dart_Handle url = Api::NewHandle(isolate, bpt->SourceUrl());
     (*bp_resolved_handler)(bpt->id(), url, bpt->LineNumber());
@@ skipping 347 matching lines @@
   for (int i = 0; i < num_libs; i++) {
     ASSERT(!lib.IsNull());
     lib_url = lib.url();
     library_list.SetAt(i, lib_url);
     lib = lib.next_registered();
   }
   return Api::NewHandle(isolate, library_list.raw());
 }
 
 }  // namespace dart