Automatically trigger installation of high-quality speech synthesis extension.

chrome/browser/chromeos/extensions/speech_synthesis_loader.h

+// Copyright (c) 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 CHROME_BROWSER_CHROMEOS_EXTENSIONS_SPEECH_SYNTHESIS_LOADER_H_
+#define CHROME_BROWSER_CHROMEOS_EXTENSIONS_SPEECH_SYNTHESIS_LOADER_H_
+
+#include "base/containers/hash_tables.h"
+#include "base/memory/weak_ptr.h"
+#include "base/prefs/pref_change_registrar.h"
+#include "chrome/browser/extensions/external_loader.h"
+#include "chrome/browser/profiles/profile.h"
+
+namespace user_prefs {
+class PrefRegistrySyncable;
+}
+
+class PrefChanceRegistrar;
+
+namespace chromeos {
+
+// Chrome OS comes with medium-quality speech synthesis extensions built-in.
+// When the user speaks a certain threshold of utterances in the same session,
+// we set a preference indicating that high quality speech is enabled for that
+// language. This class is the external extension loader that checks the
+// preference and prepares the list of external extensions to be installed
+// from the web store automatically. The high-quality speech synthesis
+// extensions are installed silently as component extensions.
+class SpeechSynthesisLoader
+    : public extensions::ExternalLoader,
+      public base::SupportsWeakPtr<SpeechSynthesisLoader> {
+ public:
+  explicit SpeechSynthesisLoader(Profile* profile);
+  virtual ~SpeechSynthesisLoader();
+
+  // Implementation of extensions::ExternalLoader:
+  virtual void StartLoading() OVERRIDE;
+
+  // Register speech synthesis prefs for a profile.
+  static void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry);
+
+ private:
+  // The profile that this loader is associated with. It listens for
+  // preference changes for that profile.
+  Profile* profile_;

[Dmitry Polukhin, 2013/12/05 18:35:32]

Need to find out how to make it work with multiprofile. Do we want to enable
spoken feedback for all profile in session or keep it per profile?

[dmazzoni, 2013/12/05 23:19:47]

Currently TTS is all done per-profile - even on desktop Chrome, if you install a
new TTS voice from the web store in one profile, another profile opened in a
different window won't use it. I think it's unlikely this will affect very many
users negatively in practice, but if we change it, we should fix it throughout
the TTS system.

My understanding is that sometime later we'll have the ability for the same
extension installed in another profile to share the same storage - is that still
the plan? If so, I think that provides a bigger benefit.

[Dmitry Polukhin, 2013/12/05 23:29:19]

On Chrome OS accessibility UI is available from system tray. So it is kind of
system wide... Anyway it not something that needs to be fixed in this CL. I just
wondering how it should work.

[dmazzoni, 2013/12/05 23:39:04]

Yes, but speech synthesis is a service available to more than just accessibility
- there are other talking apps that use the same (public) extension API, and in
M33 we now have a public speech synthesis API for the web, so we expect more
talking web sites.

This feature will apply to them too, i.e. to anyone who uses speech - that's why
I set the threshold reasonably high at 100 utterances in a single session.

+
+  // The pref change registrar, so we can watch for pref changes.
+  scoped_ptr<PrefChangeRegistrar> pref_change_registrar_;
+
+  // A weak ptr factory, so we can safely bind pref change registrar
+  // callbacks to this class.
+  base::WeakPtrFactory<SpeechSynthesisLoader> weak_ptr_factory_;
+
+  // A map from language code to the extension id of the high-quality
+  // extension for that language in the web store, if any.
+  base::hash_map<std::string, std::string> lang_to_extension_id_map_;
+
+  DISALLOW_COPY_AND_ASSIGN(SpeechSynthesisLoader);
+};
+
+}  // namespace chromeos
+
+#endif  // CHROME_BROWSER_CHROMEOS_EXTENSIONS_SPEECH_SYNTHESIS_LOADER_H_