[debug] Disable debug events if JS execution is disallowed

We cannot generate debug events if JS execution is disallowed since
vital debugging logic is still implemented in JS. Return early from
Debug::OnException if that is the case.

BUG=chromium:662674

Review-Url: https://codereview.chromium.org/2491443002
Cr-Commit-Position: refs/heads/master@{#40858}

src/debug/debug.cc

@@ -1777,6 +1777,11 @@ void Debug::OnPromiseReject(Handle<Object> promise, Handle<Object> value) {
 
 
 void Debug::OnException(Handle<Object> exception, Handle<Object> promise) {
+  // We cannot generate debug events when JS execution is disallowed.
+  // TODO(5530): Reenable debug events within DisallowJSScopes once relevant
+  // code (MakeExceptionEvent and ProcessDebugEvent) have been moved to C++.
+  if (!AllowJavascriptExecution::IsAllowed(isolate_)) return;
+
   Isolate::CatchType catch_type = isolate_->PredictExceptionCatcher();
 
   // Don't notify listener of exceptions that are internal to a desugaring.

test/debugger/debug/regress/regress-662674.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: --stack-size=100
+
+Debug = debug.Debug
+
+function overflow() {
+  return overflow();
+}
+
+Debug.setBreakOnException();
+assertThrows(overflow, RangeError);