[On-device adaptive brightness] Add AutoScreenBrightnessContinuedAdjustment flag

If this flag is enabled, auto-brightness model will continue to adapt brightness
when ambient value changes, even after user changes brightness.

The flag is meant to remain disabled, and only enabled by developers for
experiments.

Bug: 881215
Change-Id: I8ee71a6f988554e0479f420b77996687fd32685c
Reviewed-on: https://chromium-review.googlesource.com/c/1353059Reviewed-by: Dan Erat <derat@chromium.org>
Commit-Queue: Jia Meng <jiameng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611961}

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

@@ -56,6 +56,10 @@ Adapter::Adapter(Profile* profile,
     return;
   }
 
+  continue_auto_brightness_after_user_adjustment_ =
+      base::FeatureList::IsEnabled(
+          features::kAutoScreenBrightnessContinuedAdjustment);
+
   InitParams();
 }
 
@@ -95,9 +99,12 @@ void Adapter::OnUserBrightnessChanged(double old_brightness_percent,
                                       double new_brightness_percent) {}
 
 void Adapter::OnUserBrightnessChangeRequested() {
-  // This will disable |adapter_status_| so that the model will not make any
-  // brightness adjustment.
-  adapter_status_ = Status::kDisabled;
+  if (!continue_auto_brightness_after_user_adjustment_) {
+    // This will disable |adapter_status_| so that the model will not make any
+    // brightness adjustment.
+    adapter_status_ = Status::kDisabled;
+  }
+
   if (!als_init_status_)
     return;
 

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

@@ -189,6 +189,10 @@ class Adapter : public AlsReader::Observer,
 
   chromeos::PowerManagerClient* const power_manager_client_;
 
+  // Whether to continue adapting brightness after user makes a brightness
+  // change.
+  bool continue_auto_brightness_after_user_adjustment_ = false;
+
   Params params_;
 
   // This will be replaced by a mock tick clock during tests.

chromeos/chromeos_features.cc

@@ -21,6 +21,14 @@ const base::Feature kAndroidMessagesProdEndpoint{
 const base::Feature kAutoScreenBrightness{"AutoScreenBrightness",
                                           base::FEATURE_DISABLED_BY_DEFAULT};
 
+// If enabled, auto-screen-brightness model will continue to adapt brightness
+// (based on ambient light)
+// after user changes brightness. Otherwise, the model will be disabled until
+// Chrome restarts.
+const base::Feature kAutoScreenBrightnessContinuedAdjustment{
+    "AutoScreenBrightnessContinuedAdjustment",
+    base::FEATURE_DISABLED_BY_DEFAULT};
+
 // Enables or disables native ChromeVox support for Arc.
 const base::Feature kChromeVoxArcSupport{"ChromeVoxArcSupport",
                                          base::FEATURE_ENABLED_BY_DEFAULT};

chromeos/chromeos_features.h

@@ -18,6 +18,8 @@ namespace features {
 CHROMEOS_EXPORT extern const base::Feature kAndroidMessagesIntegration;
 CHROMEOS_EXPORT extern const base::Feature kAndroidMessagesProdEndpoint;
 CHROMEOS_EXPORT extern const base::Feature kAutoScreenBrightness;
+CHROMEOS_EXPORT extern const base::Feature
+    kAutoScreenBrightnessContinuedAdjustment;
 CHROMEOS_EXPORT extern const base::Feature kChromeVoxArcSupport;
 CHROMEOS_EXPORT extern const base::Feature kCrostiniFiles;
 CHROMEOS_EXPORT extern const base::Feature kCrostiniUsbSupport;