Add component for feature engagement tracking.

components/feature_engagement_tracker/public/feature_engagement_tracker.h

+// 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)

[Elliot Glaysher, 2017/03/29 21:11:39]

I'm a bit confused about where this gets compiled. Is this android only, mobile
only, or should this be compiled everywhere? If this is an EM feature, I'm
assuming this shouldn't be compiled in on the desktop builds, but looking at the
BUILD.gn files, it looks like this is compiled everywhere?

[nyquist, 2017/03/30 22:58:54]

I'll keep the compile on Linux for now to ensure that I can run tests on Linux.

However, I'll remove the code from being compiled in at the //chrome layer, and
only do that on Android.

Moved things around a little bit in the internal code to remove more ifdefs, but
this public API will have to stay to provide access to //chrome.

+
+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_