Add finch support for setting the delay before fetching prediction models.

This change allows the random delay before a fetch to the remote
Optimization Guide Service is made for prediction models and
host model features.

Bug: 1001194
Change-Id: I71a5670bb103ee67805fdc1981db9c2997e121c8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1935497Reviewed-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@{#719306}

chrome/browser/optimization_guide/prediction/prediction_manager.cc

@@ -66,14 +66,12 @@ constexpr base::TimeDelta kFetchRetryDelay = base::TimeDelta::FromMinutes(16);
 constexpr base::TimeDelta kUpdateModelsAndFeaturesDelay =
     base::TimeDelta::FromHours(24);
 
-// Provide a random time delta in seconds between |kFetchRandomMinDelay| and
-// |kFetchRandomMaxDelay|.
+// Provide a random time delta in seconds before fetching models and host model
+// features.
 base::TimeDelta RandomFetchDelay() {
-  // TODO(crbug/1027526): Add finch support for the random delay ranges.
-  constexpr int kFetchRandomMinDelaySecs = 30;
-  constexpr int kFetchRandomMaxDelaySecs = 180;
-  return base::TimeDelta::FromSeconds(
-      base::RandInt(kFetchRandomMinDelaySecs, kFetchRandomMaxDelaySecs));
+  return base::TimeDelta::FromSeconds(base::RandInt(
+      optimization_guide::features::PredictionModelFetchRandomMinDelaySecs(),
+      optimization_guide::features::PredictionModelFetchRandomMaxDelaySecs()));
 }
 
 }  // namespace

components/optimization_guide/optimization_guide_features.cc

@@ -206,5 +206,15 @@ bool ShouldOverrideOptimizationTargetDecisionForMetricsPurposes(
       kOptimizationTargetPrediction, "painful_page_load_metrics_only", false);
 }
 
+int PredictionModelFetchRandomMinDelaySecs() {
+  return GetFieldTrialParamByFeatureAsInt(kOptimizationTargetPrediction,
+                                          "fetch_random_min_delay_secs", 30);
+}
+
+int PredictionModelFetchRandomMaxDelaySecs() {
+  return GetFieldTrialParamByFeatureAsInt(kOptimizationTargetPrediction,
+                                          "fetch_random_max_delay_secs", 180);
+}
+
 }  // namespace features
 }  // namespace optimization_guide

components/optimization_guide/optimization_guide_features.h

@@ -105,6 +105,14 @@ base::TimeDelta StoredHostModelFeaturesFreshnessDuration();
 bool ShouldOverrideOptimizationTargetDecisionForMetricsPurposes(
     proto::OptimizationTarget optimization_target);
 
+// Returns the minimum number of seconds to randomly delay before starting to
+// fetch for prediction models and host model features.
+int PredictionModelFetchRandomMinDelaySecs();
+
+// Returns the maximum number of seconds to randomly delay before starting to
+// fetch for prediction models and host model features.
+int PredictionModelFetchRandomMaxDelaySecs();
+
 }  // namespace features
 }  // namespace optimization_guide