Revert "[Power ML] Change UserActivityPrediction flag to enabled"

This reverts commit 12c3b65c.

Reason for revert: Suspect for failing PowerPolicy browser_tests, https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/linux-chromeos-rel/20473

Original change's description:
> [Power ML] Change UserActivityPrediction flag to enabled
> 
> Bug: 862461
> Change-Id: I624d39293e50754629b3b30990828af73f57f0b3
> Reviewed-on: https://chromium-review.googlesource.com/c/1482281
> Reviewed-by: Dan Erat <derat@chromium.org>
> Reviewed-by: Steven Holte <holte@chromium.org>
> Commit-Queue: Jia Meng <jiameng@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#634856}

TBR=derat@chromium.org,holte@chromium.org,jiameng@chromium.org

Change-Id: Ic6cee677470af06e5ef5de8d362a2978a37291c2
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 862461, 935044
Reviewed-on: https://chromium-review.googlesource.com/c/1484821Reviewed-by: Kristi Park <kristipark@chromium.org>
Commit-Queue: Kristi Park <kristipark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634891}

chrome/browser/chromeos/power/ml/smart_dim/model_impl.cc

@@ -222,18 +222,25 @@ void LogPowerMLSmartDimParameterResult(SmartDimParameterResult result) {
   UMA_HISTOGRAM_ENUMERATION("PowerML.SmartDimParameter.Result", result);
 }
 
-// Returns "dim_threshold" from experiment parameter. Also logs status to UMA.
-float GetDimThreshold() {
-  const double default_threshold = -0.18;
-  const double dim_threshold = base::GetFieldTrialParamByFeatureAsDouble(
-      features::kUserActivityPrediction, "dim_threshold", default_threshold);
-  if (std::abs(dim_threshold - default_threshold) < 1e-10) {
-    LogPowerMLSmartDimParameterResult(
-        SmartDimParameterResult::kUseDefaultValue);
-  } else {
-    LogPowerMLSmartDimParameterResult(SmartDimParameterResult::kSuccess);
+// Returns "dim_threshold" from experiment parameter. Also logs status to UMA
+// (i.e. whether the parameter is undefined or cannot be parsed, or can be
+// parsed successfully.
+base::Optional<float> GetDimThreshold() {
+  const std::string dim_threshold_str = base::GetFieldTrialParamValueByFeature(
+      features::kUserActivityPrediction, "dim_threshold");
+  if (dim_threshold_str.empty()) {
+    LogPowerMLSmartDimParameterResult(SmartDimParameterResult::kUndefinedError);
+    return base::nullopt;
+  }
+
+  double dim_threshold_double;
+  if (!base::StringToDouble(dim_threshold_str, &dim_threshold_double)) {
+    LogPowerMLSmartDimParameterResult(SmartDimParameterResult::kParsingError);
+    return base::nullopt;
   }
-  return dim_threshold;
+
+  LogPowerMLSmartDimParameterResult(SmartDimParameterResult::kSuccess);
+  return base::Optional<float>(dim_threshold_double);
 }
 
 }  // namespace
@@ -315,12 +322,12 @@ SmartDimModelResult SmartDimModelImpl::CalculateInactivityScoreTfNative(
 UserActivityEvent::ModelPrediction
 SmartDimModelImpl::CreatePredictionFromInactivityScore(float inactivity_score) {
   UserActivityEvent::ModelPrediction prediction;
-  const float dim_threshold = GetDimThreshold();
+  const base::Optional<float> dim_threshold = GetDimThreshold();
 
-  prediction.set_decision_threshold(ScoreToProbability(dim_threshold));
+  prediction.set_decision_threshold(ScoreToProbability(dim_threshold.value()));
   prediction.set_inactivity_score(ScoreToProbability(inactivity_score));
 
-  if (inactivity_score >= dim_threshold) {
+  if (inactivity_score >= dim_threshold.value()) {
     prediction.set_response(UserActivityEvent::ModelPrediction::DIM);
   } else {
     prediction.set_response(UserActivityEvent::ModelPrediction::NO_DIM);
@@ -335,6 +342,11 @@ UserActivityEvent::ModelPrediction SmartDimModelImpl::ShouldDimTfNative(
   UserActivityEvent::ModelPrediction prediction;
   prediction.set_response(UserActivityEvent::ModelPrediction::MODEL_ERROR);
 
+  const base::Optional<float> dim_threshold = GetDimThreshold();
+  if (!dim_threshold) {
+    return prediction;
+  }
+
   float inactivity_score = 0;
   const SmartDimModelResult result =
       CalculateInactivityScoreTfNative(input_features, &inactivity_score);
@@ -356,6 +368,12 @@ void SmartDimModelImpl::ShouldDimMlService(
   UserActivityEvent::ModelPrediction prediction;
   prediction.set_response(UserActivityEvent::ModelPrediction::MODEL_ERROR);
 
+  const base::Optional<float> dim_threshold = GetDimThreshold();
+  if (!dim_threshold) {
+    std::move(callback).Run(prediction);
+    return;
+  }
+
   std::vector<float> vectorized_features;
   auto preprocess_result =
       PreprocessInput(input_features, &vectorized_features);

chrome/browser/chromeos/power/ml/smart_dim/model_impl.h

@@ -44,8 +44,7 @@ enum class SmartDimParameterResult {
   kSuccess = 0,
   kUndefinedError = 1,
   kParsingError = 2,
-  kUseDefaultValue = 3,
-  kMaxValue = kUseDefaultValue
+  kMaxValue = kParsingError
 };
 
 // Real implementation of SmartDimModel that predicts whether an upcoming screen

chrome/browser/chromeos/power/ml/smart_dim/model_unittest.cc

@@ -146,6 +146,25 @@ TEST_F(SmartDimModelImplTest, ShouldDim) {
   EXPECT_TRUE(callback_done);
 }
 
+TEST_F(SmartDimModelImplTest, ModelError) {
+  // Model parameter is undefined, which would trigger a model error.
+  bool callback_done = false;
+  smart_dim_model_.RequestDimDecision(
+      features_, base::BindOnce(
+                     [](bool* callback_done,
+                        UserActivityEvent::ModelPrediction prediction) {
+                       EXPECT_EQ(
+                           UserActivityEvent::ModelPrediction::MODEL_ERROR,
+                           prediction.response());
+                       EXPECT_FALSE(prediction.has_decision_threshold());
+                       EXPECT_FALSE(prediction.has_inactivity_score());
+                       *callback_done = true;
+                     },
+                     &callback_done));
+  scoped_task_environment_.RunUntilIdle();
+  EXPECT_TRUE(callback_done);
+}
+
 // Check that CancelableCallback ensures a callback doesn't execute twice, in
 // case two RequestDimDecision() calls were made before any callback ran.
 TEST_F(SmartDimModelImplTest, CheckCancelableCallback) {

chromeos/constants/chromeos_features.cc

@@ -80,7 +80,7 @@ const base::Feature kUseMessagesStagingUrl{"UseMessagesStagingUrl",
 // Defined here rather than in //chrome alongside other related features so that
 // PowerPolicyController can check it.
 const base::Feature kUserActivityPrediction{"UserActivityPrediction",
-                                            base::FEATURE_ENABLED_BY_DEFAULT};
+                                            base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Enables or disables ML service inferencing (instead of TFNative inferencing)
 // for the Smart Dim feature on Chrome OS.

tools/metrics/histograms/enums.xml

@@ -43318,10 +43318,6 @@ Called by update_net_trust_anchors.py.-->
   <int value="2" label="Parsing error">
     Threshold parameter was not parsed correctly from string to double.
   </int>
-  <int value="3" label="Use default value">
-    Threshold parameter was not supplied or same as the default value. In either
-    case, the default value was used.
-  </int>
 </enum>
 
 <enum name="PowerSupplyType">