Return a failure exit code in flutter_tester if an uncaught error occurs in a microtask (#5736)

lib/ui/ui_dart_state.cc

@@ -7,6 +7,7 @@
 #include "flutter/fml/message_loop.h"
 #include "flutter/lib/ui/window/window.h"
 #include "lib/tonic/converter/dart_converter.h"
+#include "lib/tonic/dart_message_handler.h"
 
 using tonic::ToDart;
 
@@ -106,4 +107,12 @@ IsolateNameServer* UIDartState::GetIsolateNameServer() {
   return isolate_name_server_;
 }
 
+tonic::DartErrorHandleType UIDartState::GetLastError() {
+  tonic::DartErrorHandleType error = message_handler().isolate_last_error();
+  if (error == tonic::kNoError) {
+    error = microtask_queue_.GetLastError();
+  }
+  return error;
+}
+
 }  // namespace blink

lib/ui/ui_dart_state.h

@@ -49,6 +49,8 @@ class UIDartState : public tonic::DartState {
 
   IsolateNameServer* GetIsolateNameServer();
 
+  tonic::DartErrorHandleType GetLastError();
+
   template <class T>
   static flow::SkiaGPUObject<T> CreateGPUObject(sk_sp<T> object) {
     if (!object) {

runtime/runtime_controller.cc

@@ -270,8 +270,7 @@ bool RuntimeController::HasLivePorts() {
 }
 
 tonic::DartErrorHandleType RuntimeController::GetLastError() {
-  return root_isolate_ ? root_isolate_->message_handler().isolate_last_error()
-                       : tonic::kNoError;
+  return root_isolate_ ? root_isolate_->GetLastError() : tonic::kNoError;
 }
 
 fml::WeakPtr<DartIsolate> RuntimeController::GetRootIsolate() {