Modify languageSettingsPrivate IDL and flesh out stub implementation

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

+// 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.
+
+#include "chrome/browser/extensions/api/language_settings_private/language_settings_private_delegate.h"
+
+#include "content/public/browser/browser_context.h"
+
+namespace extensions {
+
+namespace language_settings_private = api::language_settings_private;
+
+LanguageSettingsPrivateDelegate::LanguageSettingsPrivateDelegate(
+    content::BrowserContext* context)
+    : context_(context),
+      listening_spellcheck_(false) {
+  // Register with the event router so we know when renderers are listening to
+  // our events. We first check and see if there *is* an event router, because
+  // some unit tests try to create all context services, but don't initialize
+  // the event router first.
+  EventRouter* event_router = EventRouter::Get(context_);
+  if (!event_router)
+    return;
+
+  event_router->RegisterObserver(this,
+      language_settings_private::OnSpellcheckDictionariesChanged::kEventName);
+  event_router->RegisterObserver(this,
+      language_settings_private::OnCustomDictionaryChanged::kEventName);
+
+  StartOrStopListeningForSpellcheckChanges();
+}
+
+LanguageSettingsPrivateDelegate::~LanguageSettingsPrivateDelegate() {
+  DCHECK(!listening_spellcheck_);
+}
+
+LanguageSettingsPrivateDelegate* LanguageSettingsPrivateDelegate::Create(
+    content::BrowserContext* context) {
+  return new LanguageSettingsPrivateDelegate(context);
+}
+
+void LanguageSettingsPrivateDelegate::Shutdown() {
+  // Unregister with the event router. We first check and see if there *is* an
+  // event router, because some unit tests try to shutdown all context services,
+  // but didn't initialize the event router first.
+  EventRouter* event_router = EventRouter::Get(context_);
+  if (event_router)
+    event_router->UnregisterObserver(this);
+
+  if (listening_spellcheck_) {
+    // TODO(michaelpg): unregister observers.
+  }
+
+  listening_spellcheck_ = false;
+}
+
+void LanguageSettingsPrivateDelegate::OnListenerAdded(
+    const EventListenerInfo& details) {
+  // Start listening to spellcheck change events.
+  if (details.event_name ==
+      language_settings_private::OnSpellcheckDictionariesChanged::kEventName ||
+      details.event_name ==
+      language_settings_private::OnCustomDictionaryChanged::kEventName) {
+    StartOrStopListeningForSpellcheckChanges();
+  }
+}
+
+void LanguageSettingsPrivateDelegate::OnListenerRemoved(
+    const EventListenerInfo& details) {
+  // Stop listening to events if there are no more listeners.
+  StartOrStopListeningForSpellcheckChanges();
+}
+
+void LanguageSettingsPrivateDelegate::
+    StartOrStopListeningForSpellcheckChanges() {
+  EventRouter* event_router = EventRouter::Get(context_);
+  bool should_listen =
+      event_router->HasEventListener(language_settings_private::
+          OnSpellcheckDictionariesChanged::kEventName) ||
+      event_router->HasEventListener(language_settings_private::
+          OnCustomDictionaryChanged::kEventName);
+
+  if (should_listen && !listening_spellcheck_) {
+    // TODO: register observers.
+  } else if (!should_listen && listening_spellcheck_) {
+    // TODO(michaelpg): unregister observers.
+  }
+
+  listening_spellcheck_ = should_listen;
+}
+
+}  // namespace extensions