Add device policies to control accessibility settings on the login screen

chrome/browser/chromeos/policy/recommendation_restorer.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/chromeos/policy/recommendation_restorer.h"
+
+#include "ash/shell.h"
+#include "ash/wm/user_activity_detector.h"
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/command_line.h"
+#include "base/location.h"
+#include "base/logging.h"
+#include "base/prefs/pref_service.h"
+#include "base/stl_util.h"
+#include "base/time.h"
+#include "base/values.h"
+#include "chrome/browser/chromeos/profiles/profile_helper.h"
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/common/chrome_notification_types.h"
+#include "chrome/common/pref_names.h"
+#include "chromeos/chromeos_switches.h"
+#include "content/public/browser/notification_details.h"
+#include "content/public/browser/notification_service.h"
+#include "content/public/browser/notification_source.h"
+
+namespace policy {
+
+namespace {
+  // The amount of idle time after which recommended values are restored.
+  const int kRestoreDelayInMs = 60 * 1000;  // 1 minute.
+}  // namespace
+
+RecommendationRestorerInternal::RecommendationRestorerInternal(
+    PrefService* prefs) {
+  registrar_.Init(prefs);
+  registrar_.Add(prefs::kLargeCursorEnabled,
+                 base::Bind(&RecommendationRestorerInternal::CheckPref,
+                            base::Unretained(this)));
+  registrar_.Add(prefs::kSpokenFeedbackEnabled,
+                 base::Bind(&RecommendationRestorerInternal::CheckPref,
+                            base::Unretained(this)));
+  registrar_.Add(prefs::kHighContrastEnabled,
+                 base::Bind(&RecommendationRestorerInternal::CheckPref,
+                            base::Unretained(this)));
+  registrar_.Add(prefs::kScreenMagnifierEnabled,
+                 base::Bind(&RecommendationRestorerInternal::CheckPref,
+                            base::Unretained(this)));
+  registrar_.Add(prefs::kScreenMagnifierType,
+                 base::Bind(&RecommendationRestorerInternal::CheckPref,
+                            base::Unretained(this)));
+
+  RestoreAll();
+}
+
+RecommendationRestorerInternal::~RecommendationRestorerInternal() {
+  if (ash::Shell::HasInstance())
+    ash::Shell::GetInstance()->user_activity_detector()->RemoveObserver(this);
+
+  STLDeleteValues(&recommended_values_);
+}
+
+void RecommendationRestorerInternal::OnUserActivity() {
+  if (restore_timer_.IsRunning())
+    restore_timer_.Reset();
+}
+
+void RecommendationRestorerInternal::CheckPref(
+    const std::string& pref_name) {
+  const PrefService::Preference* pref =
+      registrar_.prefs()->FindPreference(pref_name.c_str());
+  if (!pref) {
+    NOTREACHED();
+    return;
+  }
+
+  const base::Value* recommended_value = pref->GetRecommendedValue();
+  if (!recommended_value) {
+    std::map<std::string, base::Value*>::iterator recommended_value_entry =
+        recommended_values_.find(pref->name());
+    if (recommended_value_entry != recommended_values_.end()) {
+      delete recommended_value_entry->second;
+      recommended_values_.erase(recommended_value_entry);
+    }
+    return;
+  }
+
+  base::Value*& recommended_value_entry = recommended_values_[pref->name()];
+  if (!base::Value::Equals(recommended_value, recommended_value_entry)) {

[Mattias Nissler (ping if slow), 2013/06/12 13:55:16]

So this recommended_values_ thing is just here to detect whether the pref change
was user-triggered, instead of admin-triggered?

Can't you just ignore pref changes entirely here and just call ClearPref() on
all prefs when the timer expires? I don't see what would be wrong with that.

[bartfab (slow), 2013/06/12 18:57:49]

No, the |recommended_values_| are here so that I can detect changes to
recommended values. Whenever that happens (when a new policy kicks in or a
policy is modified), I want to restore immediately. When there is a
user-initiated change, I want to start the timer.

[Mattias Nissler (ping if slow), 2013/06/13 18:11:46]

I think a better implementation for this would be to have PrefService fire a
change notification for the recommended value change (it currently filters it if
the effective value doesn't change).

Then again, why would you want to reset immediately if the policy changes?
UX-wise that's probably worse than just switching to the new default when the
timer fires. If there's no user setting, the switch happens immediately, which
is also fine. So why the complexity to support the behavior you describe?

+    delete recommended_value_entry;
+    recommended_value_entry = recommended_value->DeepCopy();
+    PrefService* prefs = registrar_.prefs();
+    prefs->ClearPref(pref->name().c_str());
+    return;
+  }
+
+  if (!pref->HasUserSetting())
+    return;
+
+  // Listen for user activity so that the timer can be reset while the user is
+  // active, causing it to fire only when the user remains idle for
+  // |kRestoreDelayInMs|.
+  if (ash::Shell::HasInstance()) {
+    ash::UserActivityDetector* user_activity_detector =
+        ash::Shell::GetInstance()->user_activity_detector();
+    if (!user_activity_detector->HasObserver(this))
+      user_activity_detector->AddObserver(this);
+  }
+
+  // A single timer is sufficient as every pref changed initiated by the user
+  // implies user activity, meaning that even if there was a separate timer per
+  // pref, they would all be reset at this point, causing them to fire at
+  // exactly the same time.
+  restore_timer_.Start(
+      FROM_HERE,
+      base::TimeDelta::FromMilliseconds(kRestoreDelayInMs),
+      base::Bind(&RecommendationRestorerInternal::RestoreAll,
+                 base::Unretained(this)));
+}
+
+void RecommendationRestorerInternal::RestoreAll() {
+  STLDeleteValues(&recommended_values_);
+
+  CheckPref(prefs::kLargeCursorEnabled);
+  CheckPref(prefs::kSpokenFeedbackEnabled);
+  CheckPref(prefs::kHighContrastEnabled);
+  CheckPref(prefs::kScreenMagnifierEnabled);
+  CheckPref(prefs::kScreenMagnifierType);
+}
+
+RecommendationRestorer::RecommendationRestorer(Profile* profile) {
+  if (!chromeos::ProfileHelper::IsSigninProfile(profile))
+    return;
+
+  // Recommended values are restored in the login profile while the login screen
+  // is being shown. If this is a restart after a browser crash inside a user
+  // session, do nothing.
+  if (!CommandLine::ForCurrentProcess()->HasSwitch(
+          chromeos::switches::kLoginManager)) {

[Mattias Nissler (ping if slow), 2013/06/12 13:55:16]

So IsIsgninProfile returns true in the restart case? That seems a bug to me?

[bartfab (slow), 2013/06/12 18:57:49]

IsSigninProfile returns true when the BCKS is created for the login profile. A
login profile is always instantiated in the background. IIRC, it is used for
things beyond the login screen. Hence, it always exists.

[Mattias Nissler (ping if slow), 2013/06/13 18:11:46]

So you're saying the accessibility code picks up pref values from the login
profile even if a session is running? I'm just trying to understand what would
go wrong if this check got removed. The comment doesn't really help...

+    return;
+  }
+
+  // Create an object that will handle the actual restoring of recommended
+  // values.
+  recommendation_restorer_internal_.reset(new RecommendationRestorerInternal(
+      profile->GetPrefs()));
+
+  // Subscribe to login notifications so that the restoring can be stopped when
+  // a user session begins.
+  registrar_.Add(this, chrome::NOTIFICATION_LOGIN_USER_CHANGED,
+                 content::NotificationService::AllSources());
+}
+
+RecommendationRestorer::~RecommendationRestorer() {
+}
+
+void RecommendationRestorer::Shutdown() {
+  recommendation_restorer_internal_.reset();
+}
+
+void RecommendationRestorer::Observe(
+    int type,
+    const content::NotificationSource& source,
+    const content::NotificationDetails& details) {
+  if (type == chrome::NOTIFICATION_LOGIN_USER_CHANGED) {
+    // Stop restoring recommended values in the login profile when a user
+    // session begins.
+    recommendation_restorer_internal_.reset();
+    registrar_.RemoveAll();
+  } else {
+    NOTREACHED();
+  }
+}
+
+}  // namespace policy