[inspector] Fix async stepping throw extension code.

When async stepping through code where only extension scripts are on the
stack, we the iterator is not gonna yield any frames, since it ignores
all extension frames.

Bug: chromium:1045863
Change-Id: Ifdb966e47bf1d090fa695d066003c7aff343f658
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2033167
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Auto-Submit: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66069}

src/inspector/v8-debugger.cc

@@ -295,7 +295,10 @@ bool V8Debugger::asyncStepOutOfFunction(int targetContextGroupId,
                                         bool onlyAtReturn) {
   v8::HandleScope handleScope(m_isolate);
   auto iterator = v8::debug::StackTraceIterator::Create(m_isolate);
-  CHECK(!iterator->Done());
+  // When stepping through extensions code, it is possible that the
+  // iterator doesn't have any frames, since we exclude all frames
+  // that correspond to extension scripts.
+  if (iterator->Done()) return false;
   bool atReturn = !iterator->GetReturnValue().IsEmpty();
   iterator->Advance();
   // Synchronous stack has more then one frame.