[PowerML] Add kPowerSmartDimEnabled pref and use it in smart dim model.

This pref will control whether smart dim should be enabled for a user. The
default value is true (i.e. Enabled). The next cl will add policy so that
enterprise users can enforce a different policy.

As this is a power-related pref, it is added to power_prefs[.h|.cc].
However as there is no need to send its value to powerd, it is
intentionally left out of PowerPrefs::UpdatePowerPolicyFromPrefs.

Bug: 862461
Change-Id: Ibaa705362c9951aecae78d9ce28780651067a6ea
Reviewed-on: https://chromium-review.googlesource.com/1166266Reviewed-by: Dan Erat <derat@chromium.org>
Commit-Queue: Jia Meng <jiameng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581435}

ash/public/cpp/ash_pref_names.cc

@@ -225,6 +225,9 @@ const char kPowerWaitForInitialUserActivity[] =
 const char kPowerForceNonzeroBrightnessForUserActivity[] =
     "power.force_nonzero_brightness_for_user_activity";
 
+// Boolean controlling whether smart dim model is enabled.
+const char kPowerSmartDimEnabled[] = "power.smart_dim_enabled";
+
 // |kShelfAlignment| and |kShelfAutoHideBehavior| have a local variant. The
 // local variant is not synced and is used if set. If the local variant is not
 // set its value is set from the synced value (once prefs have been

ash/public/cpp/ash_pref_names.h

@@ -87,6 +87,7 @@ ASH_PUBLIC_EXPORT extern const char kPowerUserActivityScreenDimDelayFactor[];
 ASH_PUBLIC_EXPORT extern const char kPowerWaitForInitialUserActivity[];
 ASH_PUBLIC_EXPORT extern const char
     kPowerForceNonzeroBrightnessForUserActivity[];
+ASH_PUBLIC_EXPORT extern const char kPowerSmartDimEnabled[];
 
 ASH_PUBLIC_EXPORT extern const char kShelfAlignment[];
 ASH_PUBLIC_EXPORT extern const char kShelfAlignmentLocal[];

ash/system/power/power_prefs.cc

@@ -98,6 +98,8 @@ void RegisterProfilePrefs(PrefRegistrySimple* registry, bool for_test) {
   registry->RegisterBooleanPref(
       prefs::kPowerForceNonzeroBrightnessForUserActivity, true,
       PrefRegistry::PUBLIC);
+  registry->RegisterBooleanPref(prefs::kPowerSmartDimEnabled, true,
+                                PrefRegistry::PUBLIC);
 
   if (for_test) {
     registry->RegisterBooleanPref(prefs::kAllowScreenLock, true,
@@ -296,6 +298,7 @@ void PowerPrefs::ObservePrefs(PrefService* prefs) {
   pref_change_registrar_->Add(
       prefs::kPowerForceNonzeroBrightnessForUserActivity, update_callback);
   pref_change_registrar_->Add(prefs::kAllowScreenLock, update_callback);
+  pref_change_registrar_->Add(prefs::kPowerSmartDimEnabled, update_callback);
 
   UpdatePowerPolicyFromPrefs();
 }

ash/system/power/power_prefs_unittest.cc

@@ -264,4 +264,10 @@ TEST_F(PowerPrefsTest, DisabledLockScreen) {
             GetCurrentPowerPolicyActions());
 }
 
+TEST_F(PowerPrefsTest, SmartDimEnabled) {
+  PrefService* prefs =
+      Shell::Get()->session_controller()->GetActivePrefService();
+  EXPECT_TRUE(prefs->GetBoolean(prefs::kPowerSmartDimEnabled));
+}
+
 }  // namespace ash

chrome/browser/chromeos/power/ml/user_activity_manager.cc

@@ -6,10 +6,13 @@
 
 #include <cmath>
 
+#include "ash/public/cpp/ash_pref_names.h"
 #include "base/metrics/field_trial_params.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/strings/string_number_conversions.h"
 #include "chrome/browser/chromeos/power/ml/real_boot_clock.h"
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/profiles/profile_manager.h"
 #include "chrome/browser/resource_coordinator/tab_metrics_logger.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_list.h"
@@ -235,7 +238,16 @@ void UserActivityManager::OnIdleEventObserved(
   screen_off_occurred_ = false;
   screen_lock_occurred_ = false;
   ExtractFeatures(activity_data);
-  if (base::FeatureList::IsEnabled(features::kUserActivityPrediction) &&
+  // Default is to enable smart dim, unless user profile specifically says
+  // otherwise.
+  bool smart_dim_enabled = true;
+  const Profile* const profile = ProfileManager::GetActiveUserProfile();
+  if (profile) {
+    smart_dim_enabled =
+        profile->GetPrefs()->GetBoolean(ash::prefs::kPowerSmartDimEnabled);
+  }
+  if (smart_dim_enabled &&
+      base::FeatureList::IsEnabled(features::kUserActivityPrediction) &&
       smart_dim_model_) {
     // Decide whether to defer the imminent screen dim.
     UserActivityEvent::ModelPrediction model_prediction =