Deliver errors from devtools API calls to callbacks

headless/lib/browser/headless_devtools_client_impl.cc

Index: headless/lib/browser/headless_devtools_client_impl.cc
diff --git a/headless/lib/browser/headless_devtools_client_impl.cc b/headless/lib/browser/headless_devtools_client_impl.cc
index 22f52946e4969707b50dac9e77528cb9fe6b6065..b6e2905a405e8823c552ad6408b1668aa4763412 100644
--- a/headless/lib/browser/headless_devtools_client_impl.cc
+++ b/headless/lib/browser/headless_devtools_client_impl.cc
@@ -126,11 +126,16 @@ bool HeadlessDevToolsClientImpl::DispatchMessageReply(
   pending_messages_.erase(it);
   if (!callback.callback_with_result.is_null()) {
     const base::DictionaryValue* result_dict;
-    if (!message_dict.GetDictionary("result", &result_dict)) {
-      NOTREACHED() << "Badly formed reply result";
+    if (message_dict.GetDictionary("result", &result_dict)) {
+      callback.callback_with_result.Run(*result_dict);
+    } else if (message_dict.GetDictionary("error", &result_dict)) {
+      std::unique_ptr<base::Value> null_value = base::Value::CreateNullValue();
+      DLOG(ERROR) << "Error in method call result: " << *result_dict;
+      callback.callback_with_result.Run(*null_value);
+    } else {
+      NOTREACHED() << "Reply has neither result nor error";
       return false;
     }
-    callback.callback_with_result.Run(*result_dict);
   } else if (!callback.callback.is_null()) {
     callback.callback.Run();
   }