Add API for observing changes to the model file in the Opt Guide

Bug: 1146151
Change-Id: If63c626ce0ef01d86d7465a0715cfea7470a3ec5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2552886Reviewed-by: Michael Crouse <mcrouse@chromium.org>
Commit-Queue: Sophie Chang <sophiechang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#829882}

chrome/browser/optimization_guide/optimization_guide_keyed_service.cc

@@ -210,6 +210,20 @@ void OptimizationGuideKeyedService::ShouldTargetNavigationAsync(
       optimization_target, std::move(callback), target_decision);
 }
 
+void OptimizationGuideKeyedService::AddObserverForOptimizationTargetModel(
+    optimization_guide::proto::OptimizationTarget optimization_target,
+    optimization_guide::OptimizationTargetModelObserver* observer) {
+  // TODO(crbug/1146151): Passthrough to prediction manager.
+  NOTREACHED();
+}
+
+void OptimizationGuideKeyedService::RemoveObserverForOptimizationTargetModel(
+    optimization_guide::proto::OptimizationTarget optimization_target,
+    optimization_guide::OptimizationTargetModelObserver* observer) {
+  // TODO(crbug/1146151): Passthrough to prediction manager.
+  NOTREACHED();
+}
+
 void OptimizationGuideKeyedService::RegisterOptimizationTypes(
     const std::vector<optimization_guide::proto::OptimizationType>&
         optimization_types) {

chrome/browser/optimization_guide/optimization_guide_keyed_service.h

@@ -62,6 +62,12 @@ class OptimizationGuideKeyedService
                            float>& client_model_feature_values,
       optimization_guide::OptimizationGuideTargetDecisionCallback callback)
       override;
+  void AddObserverForOptimizationTargetModel(
+      optimization_guide::proto::OptimizationTarget optimization_target,
+      optimization_guide::OptimizationTargetModelObserver* observer) override;
+  void RemoveObserverForOptimizationTargetModel(
+      optimization_guide::proto::OptimizationTarget optimization_target,
+      optimization_guide::OptimizationTargetModelObserver* observer) override;
   void RegisterOptimizationTypes(
       const std::vector<optimization_guide::proto::OptimizationType>&
           optimization_types) override;

components/optimization_guide/BUILD.gn

@@ -52,6 +52,7 @@ static_library("optimization_guide") {
     "optimization_guide_util.h",
     "optimization_metadata.cc",
     "optimization_metadata.h",
+    "optimization_target_model_observer.h",
     "prediction_model.cc",
     "prediction_model.h",
     "store_update_data.cc",

components/optimization_guide/optimization_guide_decider.h

@@ -11,6 +11,7 @@
 #include "base/containers/flat_map.h"
 #include "base/optional.h"
 #include "components/optimization_guide/optimization_metadata.h"
+#include "components/optimization_guide/optimization_target_model_observer.h"
 #include "components/optimization_guide/proto/hints.pb.h"
 #include "components/optimization_guide/proto/models.pb.h"
 
@@ -68,6 +69,27 @@ class OptimizationGuideDecider {
           client_model_feature_values,
       OptimizationGuideTargetDecisionCallback callback) = 0;
 
+  // Adds an observer for updates to the model for |optimization_target|.
+  //
+  // It is assumed that any model retrieved this way will be passed to the
+  // Machine Learning Service for inference.
+  //
+  // Still being implemented - DO NOT USE YET.
+  virtual void AddObserverForOptimizationTargetModel(
+      proto::OptimizationTarget optimization_target,
+      OptimizationTargetModelObserver* observer) = 0;
+
+  // Removes an observer for updates to the model for |optimization_target|.
+  //
+  // If |observer| is registered for multiple targets, |observer| must be
+  // removed for all targets that it is added for in order for it to be fully
+  // removed from receiving any calls.
+  //
+  // Still being implemented - DO NOT USE YET.
+  virtual void RemoveObserverForOptimizationTargetModel(
+      proto::OptimizationTarget optimization_target,
+      OptimizationTargetModelObserver* observer) = 0;
+
   // Registers the optimization types that intend to be queried during the
   // session. It is expected for this to be called after the browser has been
   // initialized.

components/optimization_guide/optimization_target_model_observer.h

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef COMPONENTS_OPTIMIZATION_GUIDE_OPTIMIZATION_TARGET_MODEL_OBSERVER_H_
+#define COMPONENTS_OPTIMIZATION_GUIDE_OPTIMIZATION_TARGET_MODEL_OBSERVER_H_
+
+#include "base/files/file_path.h"
+#include "base/observer_list_types.h"
+#include "components/optimization_guide/proto/models.pb.h"
+
+namespace optimization_guide {
+
+// Observes |optimization_guide::OptimizationGuideDecider| for updates to models
+// for a particular optimization target.
+class OptimizationTargetModelObserver : public base::CheckedObserver {
+ public:
+  // Invoked when a model for |optimization_target| has been updated. It is
+  // guaranteed that this method will only be invoked for targets that |this|
+  // is added as an observer for.
+  //
+  // When this observer is first added, it will call this function with the
+  // file path it already has on device, if applicable.
+  virtual void OnModelFileUpdated(proto::OptimizationTarget optimization_target,
+                                  const base::FilePath& file_path) = 0;
+};
+
+}  // namespace optimization_guide
+
+#endif  // COMPONENTS_OPTIMIZATION_GUIDE_OPTIMIZATION_TARGET_MODEL_OBSERVER_H_

components/optimization_guide/test_optimization_guide_decider.cc

@@ -34,6 +34,14 @@ void TestOptimizationGuideDecider::CanApplyOptimizationAsync(
                           /*optimization_metadata=*/{});
 }
 
+void TestOptimizationGuideDecider::AddObserverForOptimizationTargetModel(
+    optimization_guide::proto::OptimizationTarget optimization_target,
+    optimization_guide::OptimizationTargetModelObserver* observer) {}
+
+void TestOptimizationGuideDecider::RemoveObserverForOptimizationTargetModel(
+    optimization_guide::proto::OptimizationTarget optimization_target,
+    optimization_guide::OptimizationTargetModelObserver* observer) {}
+
 OptimizationGuideDecision TestOptimizationGuideDecider::CanApplyOptimization(
     const GURL& url,
     proto::OptimizationType optimization_type,

components/optimization_guide/test_optimization_guide_decider.h

@@ -29,6 +29,12 @@ class TestOptimizationGuideDecider : public OptimizationGuideDecider {
       const base::flat_map<proto::ClientModelFeature, float>&
           client_model_feature_values,
       OptimizationGuideTargetDecisionCallback callback) override;
+  void AddObserverForOptimizationTargetModel(
+      proto::OptimizationTarget optimization_target,
+      OptimizationTargetModelObserver* observer) override;
+  void RemoveObserverForOptimizationTargetModel(
+      proto::OptimizationTarget optimization_target,
+      OptimizationTargetModelObserver* observer) override;
   void RegisterOptimizationTypes(
       const std::vector<proto::OptimizationType>& optimization_types) override;
   void CanApplyOptimizationAsync(