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

gin/modules/file_module_provider.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef GIN_MODULES_FILE_MODULE_PROVIDER_H_
 #define GIN_MODULES_FILE_MODULE_PROVIDER_H_
 
 #include <set>
 #include <string>
 #include <vector>
 
+#include "base/callback.h"
 #include "base/files/file_path.h"
+#include "base/memory/weak_ptr.h"
 #include "gin/gin_export.h"
 #include "gin/runner.h"
 
 namespace gin {
 
 // FileModuleProvider knows how to load AMD modules off disk. It searches for
 // modules in the directories indiciated by |search_paths|. Although we still
 // read from the file system on the main thread, we'll eventually want to move
 // the reads to a background thread.
 class GIN_EXPORT FileModuleProvider {
  public:
   explicit FileModuleProvider(
       const std::vector<base::FilePath>& search_paths);
   ~FileModuleProvider();
 
   // Searches for modules with |ids| in the file system. If found, the modules
   // will be executed asynchronously by |runner|.
-  void AttempToLoadModules(Runner* runner, const std::set<std::string>& ids);
+  void AttemptToLoadModules(Runner* runner, const std::set<std::string>& ids);
+
+  void set_completion_callback(
+      base::Callback<void(const std::set<std::string>&)> callback) {
+    completion_callback_ = callback;
+  }
+  void reset_completion_callback() {
+    completion_callback_.Reset();
+  }
 
  private:
+  void OnReadCompleted(const std::string& id, bool success);
+
+  base::WeakPtrFactory<FileModuleProvider> weak_factory_;
+
   std::vector<base::FilePath> search_paths_;
 
   // We'll only search for a given module once. We remember the set of modules
   // we've already looked for in |attempted_ids_|.
   std::set<std::string> attempted_ids_;
 
+  // The set of modules that have succeeded or failed to load.
+  std::set<std::string> successful_ids_;
+  std::set<std::string> failed_ids_;
+
+  base::Callback<void(const std::set<std::string>&)> completion_callback_;
+
   DISALLOW_COPY_AND_ASSIGN(FileModuleProvider);
 };
 
 }  // namespace gin
 
 #endif  // GIN_MODULES_FILE_MODULE_PROVIDER_H_