Mojo: Log an error when we fail to find a JS module.

gin/modules/module_runner_delegate.h

Index: gin/modules/module_runner_delegate.h
diff --git a/gin/modules/module_runner_delegate.h b/gin/modules/module_runner_delegate.h
index 09d4582dd76684ac420619104e6426f7de25203c..a2d73ae5a5510f64e041d6d3c88d9e40044e5ef5 100644
--- a/gin/modules/module_runner_delegate.h
+++ b/gin/modules/module_runner_delegate.h
@@ -40,8 +40,12 @@ class GIN_EXPORT ModuleRunnerDelegate : public ShellRunnerDelegate {
   virtual void DidCreateContext(ShellRunner* runner) OVERRIDE;
   virtual void DidRunScript(ShellRunner* runner) OVERRIDE;
 
+  // Callback for when module_provider_ finishes reading from disk.
+  void DidLoadFileModules(const std::set<std::string>& loaded_modules);
+
   BuiltinModuleMap builtin_modules_;
   FileModuleProvider module_provider_;
+  std::set<std::string> unsatisfied_dependencies_;
 
   DISALLOW_COPY_AND_ASSIGN(ModuleRunnerDelegate);
 };