Improve DartLoader error handling.

sky/engine/core/script/dart_loader.h

Index: sky/engine/core/script/dart_loader.h
diff --git a/sky/engine/core/script/dart_loader.h b/sky/engine/core/script/dart_loader.h
index 188ddb5fda21c65fcc9a0f70b80f8c31f0309502..078712ab1dd3e5d60e62715e54eca3d99bfc6145 100644
--- a/sky/engine/core/script/dart_loader.h
+++ b/sky/engine/core/script/dart_loader.h
@@ -43,6 +43,7 @@ class DartLoader {
   }
 
   DartState* dart_state() const { return dart_state_.get(); }
+  bool saw_error() const { return saw_error_; }
 
  private:
   class Job;
@@ -55,12 +56,14 @@ class DartLoader {
   Dart_Handle Source(Dart_Handle library, Dart_Handle url);
   void DidCompleteImportJob(ImportJob* job, const Vector<uint8_t>& buffer);
   void DidCompleteSourceJob(SourceJob* job, const Vector<uint8_t>& buffer);
+  void DidFailJob(Job* job);
 
   base::WeakPtr<DartState> dart_state_;
   HashMap<String, Job*> pending_libraries_;
   HashSet<OwnPtr<Job>> jobs_;
   HashSet<OwnPtr<DependencyWatcher>> dependency_watchers_;
   DartDependencyCatcher* dependency_catcher_;
+  bool saw_error_;
 
   DISALLOW_COPY_AND_ASSIGN(DartLoader);
 };