[Hotword] Delay checking for audio devices until needed.

chrome/browser/search/hotword_service_factory.cc

 // 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.
 
 #include "chrome/browser/search/hotword_service_factory.h"
 
 #include "base/prefs/pref_service.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/search/hotword_service.h"
 #include "chrome/common/pref_names.h"
@@ skipping 34 matching lines @@
   if (!hotword_service)
     return 0;
   return hotword_service->error_message();
 }
 
 // static
 bool HotwordServiceFactory::IsMicrophoneAvailable() {
   return GetInstance()->microphone_available();
 }
 
+// static
+bool HotwordServiceFactory::IsAudioDeviceStateUpdated() {
+  return GetInstance()->audio_device_state_updated();
+}
+
 HotwordServiceFactory::HotwordServiceFactory()
     : BrowserContextKeyedServiceFactory(
         "HotwordService",
         BrowserContextDependencyManager::GetInstance()),
-      microphone_available_(false) {
+      microphone_available_(false),
+      audio_device_state_updated_(false) {
   // No dependencies.
 
   // Register with the device observer list to update the microphone
   // availability.
   BrowserThread::PostTask(
       BrowserThread::UI, FROM_HERE,
       base::Bind(&HotwordServiceFactory::InitializeMicrophoneObserver,
                  base::Unretained(this)));
 }
 
 HotwordServiceFactory::~HotwordServiceFactory() {
 }
 
 void HotwordServiceFactory::InitializeMicrophoneObserver() {
   MediaCaptureDevicesDispatcher::GetInstance()->AddObserver(this);
 }
 
 void HotwordServiceFactory::OnUpdateAudioDevices(
     const content::MediaStreamDevices& devices) {
   microphone_available_ = !devices.empty();
+  audio_device_state_updated_ = true;
 }
 
 void HotwordServiceFactory::UpdateMicrophoneState() {
   // In order to trigger the monitor, just call getAudioCaptureDevices.
   content::MediaStreamDevices devices =
-      MediaCaptureDevicesDispatcher::GetInstance()->GetAudioCaptureDevices();
-
-  // If the monitor had not previously been started, there may be 0 devices
-  // even if that is not accurate. However, we can update the microphone
-  // availability state now. Either the number of devices will be correct or
-  // we know that the call above will start the monitor and the microphone
-  // state will be updated very soon and call OnUpdateAudioDevices.
-  OnUpdateAudioDevices(devices);
+    MediaCaptureDevicesDispatcher::GetInstance()->GetAudioCaptureDevices();
 }
 
 void HotwordServiceFactory::RegisterProfilePrefs(
     user_prefs::PrefRegistrySyncable* prefs) {
   prefs->RegisterBooleanPref(prefs::kHotwordSearchEnabled,
                              false,
                              user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
   // Although this is default true, users will not send back information to
   // Google unless they have opted-in to Hotwording at which point they must
   // also confirm that they wish this preference to be true or opt out of it.
   prefs->RegisterBooleanPref(prefs::kHotwordAudioLoggingEnabled,
                              true,
                              user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
   prefs->RegisterStringPref(prefs::kHotwordPreviousLanguage,
                             std::string(),
                             user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
   prefs->RegisterBooleanPref(prefs::kHotwordAlwaysOnSearchEnabled,
                              false,
                              user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
 }
 
 KeyedService* HotwordServiceFactory::BuildServiceInstanceFor(
     BrowserContext* context) const {
   return new HotwordService(Profile::FromBrowserContext(context));
 }