[inspector] prepare debug::ScopeIterator for function without context

Some API functions have no context and debug::ScopeIterator::
CreateForFunction is crashing on attempt to get context.

R=jgruber@chromium.org

Bug: chromium:759913
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I0a9861ea2d19bceff97c4394b34a8dda45222b78
Reviewed-on: https://chromium-review.googlesource.com/661789
Commit-Queue: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47981}

src/debug/debug-scope-iterator.cc

@@ -15,10 +15,13 @@ namespace v8 {
 
 std::unique_ptr<debug::ScopeIterator> debug::ScopeIterator::CreateForFunction(
     v8::Isolate* v8_isolate, v8::Local<v8::Function> v8_func) {
+  internal::Handle<internal::JSFunction> func =
+      internal::Handle<internal::JSFunction>::cast(Utils::OpenHandle(*v8_func));
+  // Blink has function objects with callable map, JS_SPECIAL_API_OBJECT_TYPE
+  // but without context on heap.
+  if (!func->has_context()) return nullptr;
   return std::unique_ptr<debug::ScopeIterator>(new internal::DebugScopeIterator(
-      reinterpret_cast<internal::Isolate*>(v8_isolate),
-      internal::Handle<internal::JSFunction>::cast(
-          Utils::OpenHandle(*v8_func))));
+      reinterpret_cast<internal::Isolate*>(v8_isolate), func));
 }
 
 std::unique_ptr<debug::ScopeIterator>
@@ -27,7 +30,6 @@ debug::ScopeIterator::CreateForGeneratorObject(
   internal::Handle<internal::Object> generator =
       Utils::OpenHandle(*v8_generator);
   DCHECK(generator->IsJSGeneratorObject());
-
   return std::unique_ptr<debug::ScopeIterator>(new internal::DebugScopeIterator(
       reinterpret_cast<internal::Isolate*>(v8_isolate),
       internal::Handle<internal::JSGeneratorObject>::cast(generator)));

src/inspector/v8-debugger.cc

@@ -582,7 +582,7 @@ v8::MaybeLocal<v8::Value> V8Debugger::getTargetScopes(
           m_isolate, v8::Local<v8::Object>::Cast(value));
       break;
   }
-
+  if (!iterator) return v8::MaybeLocal<v8::Value>();
   v8::Local<v8::Array> result = v8::Array::New(m_isolate);
   if (!result->SetPrototype(context, v8::Null(m_isolate)).FromMaybe(false)) {
     return v8::MaybeLocal<v8::Value>();