Don't show the apps page on the NTP if the app launcher is installed.

chrome/browser/extensions/app_launcher.cc

 // 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.
 
 #include "chrome/browser/extensions/app_launcher.h"
 
 #include "base/command_line.h"
 #include "base/threading/sequenced_worker_pool.h"
+#include "chrome/browser/browser_process.h"
+#include "chrome/browser/prefs/pref_service.h"
 #include "chrome/common/chrome_switches.h"
+#include "chrome/common/pref_names.h"
 #include "content/public/browser/browser_thread.h"
 
 #if defined(OS_WIN)
 #include "chrome/installer/launcher_support/chrome_launcher_support.h"
 #include "chrome/installer/util/browser_distribution.h"
 #endif
 
 namespace extensions {
 
 namespace {
 
 #if defined(OS_WIN)
+void UpdatePrefAndCallCallbackOnUI(
+    bool result,
+    const OnAppLauncherEnabledCompleted& completion_callback) {
+  PrefService* prefs = g_browser_process->local_state();
+  prefs->SetBoolean(prefs::kAppLauncherIsEnabled, result);
+  completion_callback.Run(result);
+}
+
 void IsAppLauncherInstalledOnBlockingPool(
     const OnAppLauncherEnabledCompleted& completion_callback) {
   DCHECK(content::BrowserThread::GetBlockingPool()->RunsTasksOnCurrentThread());
   bool result = chrome_launcher_support::IsAppLauncherPresent();
-  content::BrowserThread::PostTask(content::BrowserThread::UI,
-                                   FROM_HERE,
-                                   base::Bind(completion_callback, result));
+  content::BrowserThread::PostTask(content::BrowserThread::UI, FROM_HERE,
+      base::Bind(UpdatePrefAndCallCallbackOnUI, result, completion_callback));
 }
 #endif
 
 }  // namespace
 
-void GetIsAppLauncherEnabled(
-    const OnAppLauncherEnabledCompleted& completion_callback) {
-  DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
-#if defined(OS_CHROMEOS)
-  completion_callback.Run(true);
+enum AppLauncherState {
+  APP_LAUNCHER_UNKNOWN,
+  APP_LAUNCHER_ENABLED,
+  APP_LAUNCHER_DISABLED,
+};
+
+AppLauncherState SynchronousAppLauncherChecks() {
+#if defined(USE_ASH)
+  return APP_LAUNCHER_ENABLED;
 #elif !defined(OS_WIN)
-  completion_callback.Run(false);
+  return APP_LAUNCHER_DISABLED;
 #else
   if (CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kShowAppListShortcut)) {
-    completion_callback.Run(true);
+    return APP_LAUNCHER_ENABLED;
+  }
+
+  if (!BrowserDistribution::GetDistribution()->AppHostIsSupported())
+    return APP_LAUNCHER_DISABLED;
+
+  return APP_LAUNCHER_UNKNOWN;
+#endif
+}
+
+void UpdateIsAppLauncherEnabled(
+    const OnAppLauncherEnabledCompleted& completion_callback) {
+  DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
+
+  AppLauncherState state = SynchronousAppLauncherChecks();
+
+  if (state != APP_LAUNCHER_UNKNOWN) {
+    bool is_enabled = state == APP_LAUNCHER_ENABLED;
+    PrefService* prefs = g_browser_process->local_state();
+    prefs->SetBoolean(prefs::kAppLauncherIsEnabled, is_enabled);
+    completion_callback.Run(is_enabled);
     return;
   }
 
-  if (!BrowserDistribution::GetDistribution()->AppHostIsSupported()) {
-    completion_callback.Run(false);
-    return;
-  }
-
+#if defined(OS_WIN)
   content::BrowserThread::PostBlockingPoolTask(
       FROM_HERE,
       base::Bind(&IsAppLauncherInstalledOnBlockingPool,
                  completion_callback));
+#else
+  // SynchronousAppLauncherChecks() never returns APP_LAUNCHER_UNKNOWN on
+  // !defined(OS_WIN), so this path is never reached.
+  NOTREACHED();
 #endif
 }
 
+bool IsAppLauncherEnabled() {
+  PrefService* prefs = g_browser_process->local_state();
+  // In some tests, the prefs aren't initialised, but the NTP still needs to
+  // work.
+  if (!prefs)
+    return SynchronousAppLauncherChecks() == APP_LAUNCHER_ENABLED;
+  return prefs->GetBoolean(prefs::kAppLauncherIsEnabled);
+}
+
+namespace app_launcher {
+
+void RegisterPrefs(PrefServiceSimple* pref_service) {
+  // If it is impossible to synchronously determine whether the app launcher is
+  // enabled, assume it is disabled. Anything that needs to know the absolute
+  // truth should call UpdateIsAppLauncherEnabled().
+  //
+  // This pref is just a cache of the value from the registry from last time
+  // Chrome ran. To avoid having the NTP block on a registry check, it guesses
+  // that the value hasn't changed since last time it was checked, using this
+  // preference.
+  bool is_enabled = SynchronousAppLauncherChecks() == APP_LAUNCHER_ENABLED;
+  pref_service->RegisterBooleanPref(prefs::kAppLauncherIsEnabled, is_enabled);
+}
+
+}  // namespace app_launcher
+
 }  // namespace extensions