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

test/cctest/test-debug.cc

Index: test/cctest/test-debug.cc
diff --git a/test/cctest/test-debug.cc b/test/cctest/test-debug.cc
index 2f6cf6e9a2f0a88cca9f4f55bca09bfa802afc65..2d0b70ef0e8a3bdb76b55d5e41b13fab82554b3d 100644
--- a/test/cctest/test-debug.cc
+++ b/test/cctest/test-debug.cc
@@ -6925,6 +6925,13 @@ TEST(DebugContextIsPreservedBetweenAccesses) {
 }
 
 
+TEST(NoDebugContextWhenDebuggerDisabled) {
+  v8::HandleScope scope(CcTest::isolate());
+  v8::Local<v8::Context> context = v8::Debug::GetDebugContext();
+  CHECK(context.IsEmpty());
+}
+
+
 static v8::Handle<v8::Value> expected_callback_data;
 static void DebugEventContextChecker(const v8::Debug::EventDetails& details) {
   CHECK(details.GetEventContext() == expected_context);