EasyUnlock: Only do Bluetooth detection for chromeos.

chrome/browser/signin/easy_unlock_service.cc

 // Copyright 2014 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/signin/easy_unlock_service.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
@@ skipping 272 matching lines @@
   SetTurnOffFlowStatus(IDLE);
 }
 
 void EasyUnlockService::Initialize() {
   registrar_.Init(profile_->GetPrefs());
   registrar_.Add(
       prefs::kEasyUnlockAllowed,
       base::Bind(&EasyUnlockService::OnPrefsChanged, base::Unretained(this)));
   OnPrefsChanged();
 
+#if defined(OS_CHROMEOS)
+  // Only start Bluetooth detection for ChromeOS since the feature is
+  // only offered on ChromeOS. Enabling this on non-ChromeOS platforms
+  // previously introduced a performance regression: http://crbug.com/404482
+  // Make sure not to reintroduce a performance regression if re-enabling on
+  // additional platforms.
+  // TODO(xiyuan): Revisit when non-chromeos platforms are supported.
   bluetooth_detector_->Initialize();
+#endif  // defined(OS_CHROMEOS)
 }
 
 void EasyUnlockService::LoadApp() {
   DCHECK(IsAllowed());
 
 #if defined(GOOGLE_CHROME_BUILD)
   base::FilePath easy_unlock_path;
 #if defined(OS_CHROMEOS)
   easy_unlock_path = base::FilePath("/usr/share/chromeos-assets/easy_unlock");
 #endif  // defined(OS_CHROMEOS)
@@ skipping 60 matching lines @@
   // Make sure lock screen state set by the extension gets reset.
   screenlock_state_handler_.reset();
 
   if (GetComponentLoader(profile_)->Exists(extension_misc::kEasyUnlockAppId)) {
     extensions::ExtensionSystem* extension_system =
         extensions::ExtensionSystem::Get(profile_);
     extension_system->extension_service()->ReloadExtension(
         extension_misc::kEasyUnlockAppId);
   }
 }