Add component for feature engagement tracking.

components/feature_engagement_tracker/public/feature_engagement_tracker.h

Index: components/feature_engagement_tracker/public/feature_engagement_tracker.h
diff --git a/components/feature_engagement_tracker/public/feature_engagement_tracker.h b/components/feature_engagement_tracker/public/feature_engagement_tracker.h
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+// Copyright 2017 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_FEATURE_ENGAGEMENT_TRACKER_PUBLIC_FEATURE_ENGAGEMENT_TRACKER_H_
+#define COMPONENTS_FEATURE_ENGAGEMENT_TRACKER_PUBLIC_FEATURE_ENGAGEMENT_TRACKER_H_
+
+#include <string>
+
+#include "base/callback.h"
+#include "base/compiler_specific.h"
+#include "base/files/file_path.h"
+#include "base/memory/ref_counted.h"
+#include "base/sequenced_task_runner.h"
+#include "components/keyed_service/core/keyed_service.h"
+
+#if defined(OS_ANDROID)
+#include "base/android/jni_android.h"
+#endif  // defined(OS_ANDROID)
+
+namespace feature_engagement_tracker {
+
+// The FeatureEngagementTracker provides a backend for displaying feature
+// enlightenment or in-product help (IPH) with a clean and easy to use API to be
+// consumed by the UI frontend. The backend behaves as a black box and takes
+// input about user behavior. Whenever the frontend gives a trigger signal that
+// IPH could be displayed, the backend will provide an answer to whether it is
+// appropriate to show it or not.
+class FeatureEngagementTracker : public KeyedService {
+ public:
+#if defined(OS_ANDROID)
+  // Returns a Java object of the type FeatureEngagementTracker for the given
+  // FeatureEngagementTracker.
+  static base::android::ScopedJavaLocalRef<jobject> GetJavaObject(
+      FeatureEngagementTracker* feature_engagement_tracker);
+#endif  // defined(OS_ANDROID)
+
+  // Invoked when the tracker has been initialized. The |success| parameter
+  // indicates that the initialization was a success and it it ready to receive
+  // calls.
+  using OnInitializedCallback = base::Callback<void(bool success)>;
+
+  // The |storage_dir| is the path to where all local storage will be.
+  // The |bakground_task_runner| will be used for all disk reads and writes.
+  static FeatureEngagementTracker* Create(
+      const base::FilePath& storage_dir,
+      const scoped_refptr<base::SequencedTaskRunner>& background_task_runner);
+
+  // Must be called whenever an event related to a precondition happens.
+  virtual void Event(const std::string& feature,
+                     const std::string& precondition) = 0;
+
+  // Must be called whenever a feature has been used.
+  virtual void Used(const std::string& feature) = 0;
+
+  // This function must be called whenever the triggering condition for a
+  // specific feature happens. Returns true iff the display of feature
+  // enlightenment must happen.
+  // If |true| is returned, the caller *must* call Dismissed() when display
+  // of feature enlightenment ends.
+  virtual bool Trigger(const std::string& feature) WARN_UNUSED_RESULT = 0;
+
+  // Must be called after display of feature enlightenment finishes.
+  virtual void Dismissed() = 0;
+
+  // For features that trigger on startup, they register a callback to ensure
+  // that they are told when the tracker has been initialized.
+  virtual void AddOnInitializedCallback(OnInitializedCallback callback) = 0;
+
+ protected:
+  FeatureEngagementTracker() = default;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(FeatureEngagementTracker);
+};
+
+}  // namespace feature_engagement_tracker
+
+#endif  // COMPONENTS_FEATURE_ENGAGEMENT_TRACKER_PUBLIC_FEATURE_ENGAGEMENT_TRACKER_H_