[On-device adaptive brightness] Update default param values.

The new values are based on experiment results.

Bug: 881215
Change-Id: I0a3e4ced061902ea3097887bad7ca1dcd73384ce
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1633892Reviewed-by: Andrew Moylan <amoylan@chromium.org>
Commit-Queue: Jia Meng <jiameng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#664660}

chrome/browser/chromeos/power/auto_screen_brightness/adapter.h

@@ -86,7 +86,7 @@ class Adapter : public AlsReader::Observer,
     double darkening_log_lux_threshold = 0.6;
     double stabilization_threshold = 0.15;
 
-    ModelCurve model_curve = ModelCurve::kPersonal;
+    ModelCurve model_curve = ModelCurve::kLatest;
 
     // Average ambient value is calculated over the past
     // |auto_brightness_als_horizon|. This is only used for brightness update,

chrome/browser/chromeos/power/auto_screen_brightness/brightness_monitor_impl.h

@@ -32,7 +32,7 @@ class BrightnessMonitorImpl : public BrightnessMonitor,
   // |brightness_sample_delay_| to record the final brightness. It can be
   // configured from finch with default value set to |kBrightnessSampleDelay|.
   static constexpr base::TimeDelta kBrightnessSampleDelay =
-      base::TimeDelta::FromSeconds(5);
+      base::TimeDelta::FromSeconds(3);
 
   BrightnessMonitorImpl();
   ~BrightnessMonitorImpl() override;

chrome/browser/chromeos/power/auto_screen_brightness/gaussian_trainer.h

@@ -33,11 +33,11 @@ class GaussianTrainer : public Trainer {
     // reasonable change would be between
     // brightness_old/(1+|brightness_step_size|) and
     // brightness_old*(1+|brightness_step_size|)
-    double brightness_step_size = 0.2;
+    double brightness_step_size = 1.5;
 
     // Similar to |brightness_step_size| except it defines reasonable brightness
     // change scale between target brightness and model predicted brightness.
-    double model_brightness_step_size = 0.3;
+    double model_brightness_step_size = 2.0;
 
     // One training data point could modify all the points on the curve, but its
     // effect is greatest on the point nearest to it (as measured by difference