Revert "[translate] Add translate ranker model loader."

components/translate/core/browser/ranker_model_loader.h

-// Copyright 2016 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_TRANSLATE_CORE_BROWSER_RANKER_MODEL_LOADER_H_
-#define COMPONENTS_TRANSLATE_CORE_BROWSER_RANKER_MODEL_LOADER_H_
-
-#include <memory>
-#include <string>
-
-#include "base/callback.h"
-#include "base/memory/ref_counted.h"
-#include "base/memory/weak_ptr.h"
-#include "base/sequence_checker.h"
-
-class GURL;
-
-namespace base {
-class FilePath;
-class SequencedTaskRunner;
-}  // namespace base
-
-namespace chrome_intelligence {
-class RankerModel;
-}  // namespace chrome_intelligence
-
-namespace translate {
-
-// Enumeration denoting the outcome of an attempt to download the model. This
-// must be kept in sync with the RankerModelStatus enum in histograms.xml
-enum class RankerModelStatus {
-  OK = 0,
-  DOWNLOAD_THROTTLED = 1,
-  DOWNLOAD_FAILED = 2,
-  PARSE_FAILED = 3,
-  VALIDATION_FAILED = 4,
-  INCOMPATIBLE = 5,
-
-  // Insert new values above this line.
-  MAX
-};
-
-// If enabled, downloads a translate ranker model and uses it to determine
-// whether the user should be given a translation prompt or not.
-class RankerModelLoader {
- public:
-  // Callback to validate a ranker model on behalf of the model loader client.
-  // For example, the callback might validate that the model is compatible with
-  // the features generated when ranking translation offerings. This callback
-  // may be called on any sequence and must, therefore, be thread-safe. This
-  // callback may be invoked after the RankerModelLoader has been destroyed
-  // and must, therefore, only access memory that it can guarantee to be
-  // valid.
-  using ValidateModelCallback = base::Callback<RankerModelStatus(
-      const chrome_intelligence::RankerModel& model)>;
-
-  // Called to transfer ownership of a loaded model back to the model loader
-  // client. This will be called on the sequence on which the model loader was
-  // constructed.  This callback may be invoked after the RankerModelLoader has
-  // been destroyed and must, therefore, only access memory that it can
-  // guarantee to be valid.
-  using OnModelAvailableCallback = base::Callback<void(
-      std::unique_ptr<chrome_intelligence::RankerModel> model)>;
-
-  // |validate_model_callback| may be called on any sequence; it must be thread
-  // safe.
-  //
-  // |on_model_available_callback| will be called on the sequence on which the
-  // ranker model loader is constructed.
-  //
-  // |model_path| denotes the file path at which the model is cached. The loader
-  // will attempt to load the model from this path first, falling back to the
-  // |model_url| if the model cannot be loaded or has expired. Upon downloading
-  // a fresh model from |model_url| the model will be persisted to |model_path|
-  // for subsequent caching.
-  //
-  // |model_url| denotes the URL from which the model should be loaded, if it
-  // has not already been cached at |model_path|.
-  //
-  // |uma_prefix| will be used as a prefix for the names of all UMA metrics
-  // generated by this loader.
-  RankerModelLoader(const ValidateModelCallback& validate_model_callback,
-                    const OnModelAvailableCallback& on_model_available_callback,
-                    const base::FilePath& model_path,
-                    const GURL& model_url,
-                    const std::string& uma_prefix);
-
-  ~RankerModelLoader();
-
-  // Asynchronously initiates loading the model from the cache file path and URL
-  // previously configured.
-  void Start();
-
-  // Call this method periodically to notify the model loader the ranker is
-  // actively in use. The user's engagement with the feature is used as a proxy
-  // for network activity. If a model download is pending, this will trigger
-  // (subject to retry and frequency limits) a model download attempt.
-  void NotifyOfRankerActivity();
-
- private:
-  // The model loader backend to which the actual loading functionality is
-  // delegated.
-  class Backend;
-  friend class Backend;
-
-  // A enum to track the current loader state.
-  enum class LoaderState { NOT_STARTED, RUNNING, FINISHED };
-
-  // Helper method to forward OnModelAvailable callbacks while noting whether
-  // or not the loader has finished its work.
-  void InternalOnModelAvailable(
-      const OnModelAvailableCallback& callback,
-      std::unique_ptr<chrome_intelligence::RankerModel> model,
-      bool finished);
-
-  // Validates that ranker model loader tasks are all performed on the same
-  // sequence.
-  base::SequenceChecker sequence_checker_;
-
-  // The task runner on which backend tasks are performed.
-  const scoped_refptr<base::SequencedTaskRunner> backend_task_runner_;
-
-  // The model loader backend to which the actual loading functionality is
-  // delegated. |backend_| may outlive its RankerModelLoader. When the
-  // RankerModelLoader is destroyed, ownership of |backend_| is transferred
-  // to a delete task posted |backend_task_runner_|.
-  std::unique_ptr<Backend> backend_;
-
-  // The current state of the loader.
-  LoaderState state_ = LoaderState::NOT_STARTED;
-
-  base::WeakPtrFactory<RankerModelLoader> weak_ptr_factory_;
-
-  DISALLOW_COPY_AND_ASSIGN(RankerModelLoader);
-};
-
-}  // namespace translate
-
-#endif  // COMPONENTS_TRANSLATE_CORE_BROWSER_RANKER_MODEL_LOADER_H_