Fix crash from turning on DevTools in the middle of catch prediction

test/mjsunit/harmony/async-debug-caught-exception.js

 // Copyright 2016 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.
 
 // Flags: --allow-natives-syntax --harmony-async-await --expose-debug-as debug
 
 Debug = debug.Debug
 
 var exception = null;
 var log;
@@ skipping 103 matching lines @@
 Debug.setBreakOnUncaughtException();
 
 log = [];
 Promise.resolve().then(() => Promise.reject()).catch(() => log.push("d")); // Exception c
 %RunMicrotasks();
 assertEquals(["d"], log);
 assertNull(exception);
 
 Debug.clearBreakOnUncaughtException();
 Debug.setListener(null);
+
+// If devtools is turned on in the middle, then catch prediction
+// could be wrong (here, it mispredicts the exception as caught),
+// but shouldn't crash.
+
+log = [];
+
+var resolve;
+var turnOnListenerPromise = new Promise(r => resolve = r);
+async function confused() {
+  await turnOnListenerPromise;
+  throw foo
+}
+confused();
+Promise.resolve().then(() => {
+  Debug.setListener(listener);
+  Debug.setBreakOnUncaughtException();
+  resolve();
+});
+
+assertEquals([], log);