Update default host model features to be the unknown value.

This change sets the default value for host model features to be an value
that the prediction model can interpret as unknown (-1 in this case). This
will improve the model accuracy when host model features are unvailable
for the current navigation.

Bug: 1036025
Change-Id: Iff7dab042829a540c06854f9ea7e84e187dbc7ed
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1977189Reviewed-by: Sophie Chang <sophiechang@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Commit-Queue: Michael Crouse <mcrouse@chromium.org>
Cr-Commit-Position: refs/heads/master@{#726627}

chrome/browser/optimization_guide/prediction/prediction_manager.cc

@@ -335,7 +335,7 @@ base::flat_map<std::string, float> PredictionManager::BuildFeatureMap(
       continue;
     }
     if (!host_model_features || !host_model_features->contains(model_feature)) {
-      feature_map[model_feature] = 0.0;
+      feature_map[model_feature] = -1.0;
       continue;
     }
     feature_map[model_feature] =

chrome/browser/optimization_guide/prediction/prediction_manager_unittest.cc

@@ -62,6 +62,8 @@ std::unique_ptr<proto::PredictionModel> CreatePredictionModel() {
   model_info->set_version(1);
   model_info->add_supported_model_features(
       proto::CLIENT_MODEL_FEATURE_EFFECTIVE_CONNECTION_TYPE);
+  prediction_model->mutable_model_info()->add_supported_host_model_features(
+      "host_feat1");
   model_info->set_optimization_target(
       proto::OPTIMIZATION_TARGET_PAINFUL_PAGE_LOAD);
   model_info->add_supported_model_types(
@@ -91,6 +93,8 @@ std::unique_ptr<proto::GetModelsResponse> BuildGetModelsResponse(
     prediction_model->mutable_model_info()->add_supported_model_features(
         client_model_feature);
   }
+  prediction_model->mutable_model_info()->add_supported_host_model_features(
+      "host_feat1");
   prediction_model->mutable_model_info()->set_version(2);
   *get_models_response->add_models() = *prediction_model.get();
 
@@ -115,6 +119,8 @@ class TestPredictionModel : public PredictionModel {
     }
     *prediction_score = 0.6;
     model_evaluated_ = true;
+    last_evaluated_features_ =
+        base::flat_map<std::string, float>(model_features);
     return OptimizationTargetDecision::kPageLoadMatches;
   }
 
@@ -122,10 +128,15 @@ class TestPredictionModel : public PredictionModel {
 
   void ResetModelEvaluationState() { model_evaluated_ = false; }
 
+  base::flat_map<std::string, float> last_evaluated_features() {
+    return last_evaluated_features_;
+  }
+
  private:
   bool ValidatePredictionModel() const override { return true; }
 
   bool model_evaluated_ = false;
+  base::flat_map<std::string, float> last_evaluated_features_;
 };
 
 // A mock class implementation of TopHostProvider.
@@ -1198,6 +1209,7 @@ TEST_F(PredictionManagerTest, NoHostModelFeaturesForHost) {
       "OptimizationGuide.PredictionManager."
       "HasHostModelFeaturesForHost",
       false, 1);
+  EXPECT_LT(test_prediction_model->last_evaluated_features()["host_feat1"], 0);
 
   EXPECT_FALSE(prediction_manager()->GetHostModelFeaturesForTesting().contains(
       "bar.com"));