Modify languageSettingsPrivate IDL and flesh out stub implementation

chrome/browser/extensions/api/language_settings_private/language_settings_private_delegate.h

+// Copyright 2015 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 CHROME_BROWSER_EXTENSIONS_API_LANGUAGE_SETTINGS_PRIVATE_LANGUAGE_SETTINGS_PRIVATE_DELEGATE_H_
+#define CHROME_BROWSER_EXTENSIONS_API_LANGUAGE_SETTINGS_PRIVATE_LANGUAGE_SETTINGS_PRIVATE_DELEGATE_H_
+
+#include "chrome/common/extensions/api/language_settings_private.h"
+#include "components/keyed_service/core/keyed_service.h"
+#include "extensions/browser/event_router.h"
+
+namespace content {
+class BrowserContext;
+}
+
+namespace extensions {
+
+// Observes language settings and routes changes as events to listeners of the
+// languageSettingsPrivate API.
+class LanguageSettingsPrivateDelegate
+    : public KeyedService,
+      public EventRouter::Observer {
+ public:
+  static LanguageSettingsPrivateDelegate* Create(
+      content::BrowserContext* browser_context);
+  ~LanguageSettingsPrivateDelegate() override;
+
+ protected:
+  explicit LanguageSettingsPrivateDelegate(content::BrowserContext* context);
+
+  // KeyedService implementation.
+  void Shutdown() override;
+
+  // EventRouter::Observer implementation.
+  void OnListenerAdded(const EventListenerInfo& details) override;
+  void OnListenerRemoved(const EventListenerInfo& details) override;
+
+ private:
+  // If there are any JavaScript listeners registered for spellcheck events,
+  // ensures we are registered for change notifications. Otherwise, unregisters
+  // any observers.
+  void StartOrStopListeningForSpellcheckChanges();
+
+  content::BrowserContext* context_;
+
+  // True if there are observers listening for spellcheck events.
+  bool listening_spellcheck_;
+
+  DISALLOW_COPY_AND_ASSIGN(LanguageSettingsPrivateDelegate);
+};
+
+}  // namespace extensions
+
+#endif  // CHROME_BROWSER_EXTENSIONS_API_LANGUAGE_SETTINGS_PRIVATE_LANGUAGE_SETTINGS_PRIVATE_DELEGATE_H_