Don't create debug context if debug listener is not set

src/api.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/api.h"
 
 #include <string.h>  // For memcpy, strlen.
 #ifdef V8_USE_ADDRESS_SANITIZER
 #include <sanitizer/asan_interface.h>
 #endif  // V8_USE_ADDRESS_SANITIZER
@@ skipping 7366 matching lines @@
 
 
 void Debug::ProcessDebugMessages() {
   i::Isolate::Current()->debug()->ProcessDebugMessages(true);
 }
 
 
 Local<Context> Debug::GetDebugContext() {
   i::Isolate* isolate = i::Isolate::Current();
   ENTER_V8(isolate);
-  return Utils::ToLocal(i::Isolate::Current()->debug()->GetDebugContext());
+  return Utils::ToLocal(isolate->debug()->GetDebugContext());
 }
 
 
 void Debug::SetLiveEditEnabled(Isolate* isolate, bool enable) {
   i::Isolate* internal_isolate = reinterpret_cast<i::Isolate*>(isolate);
   internal_isolate->debug()->set_live_edit_enabled(enable);
 }
 
 
 Handle<String> CpuProfileNode::GetFunctionName() const {
@@ skipping 634 matching lines @@
   Isolate* isolate = reinterpret_cast<Isolate*>(info.GetIsolate());
   Address callback_address =
       reinterpret_cast<Address>(reinterpret_cast<intptr_t>(callback));
   VMState<EXTERNAL> state(isolate);
   ExternalCallbackScope call_scope(isolate, callback_address);
   callback(info);
 }
 
 
 } }  // namespace v8::internal