Implement a site engagement score based on time-on-site.

chrome/browser/engagement/site_engagement_helper.h

 // Copyright 2015 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 CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_HELPER_H_
 #define CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_HELPER_H_
 
 #include "base/macros.h"
+#include "base/timer/timer.h"
+#include "content/public/browser/render_view_host.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/browser/web_contents_user_data.h"
 
 namespace content {
 class WebContents;
 }
 
 class GURL;
 
 // Per-WebContents class to handle updating the site engagement scores for
-// origins as the user navigates.
+// origins based on the time spent on site.
+//
+// Time on site is recorded by detecting any user input (mouse or keypress) per
+// some discrete time unit. If there is user input, then record a positive site
+// engagement.
+//
+// TODO(dominickn): account for use cases where user input is not a good proxy
+// for time on site: e.g. watching videos.
 class SiteEngagementHelper
     : public content::WebContentsObserver,
       public content::WebContentsUserData<SiteEngagementHelper> {
  public:
   ~SiteEngagementHelper() override;
 
  private:
   explicit SiteEngagementHelper(content::WebContents* web_contents);
   friend class content::WebContentsUserData<SiteEngagementHelper>;
 
+  // Callback to register key press events from the RenderViewHost.
+  bool HandleKeyPressEvent(const content::NativeWebKeyboardEvent& event);
+
+  // Callback to register mouse events from the RenderViewHost.
+  bool HandleMouseEvent(const blink::WebMouseEvent& event);
+
+  // Callback that is fired at regular intervals to record site engagement based
+  // on user input.
+  void TimerFired();
+
+  void StartTimer();
+
   // content::WebContentsObserver overrides.
-  void DidStartNavigationToPendingEntry(
-      const GURL& url,
-      content::NavigationController::ReloadType reload_type) override;
+  void RenderViewHostChanged(content::RenderViewHost* old_host,
+                             content::RenderViewHost* new_host) override;
+
+  void WasShown() override;
+
+  void WasHidden() override;
+
+  content::RenderWidgetHost::KeyPressEventCallback key_press_event_callback_;
+  content::RenderWidgetHost::MouseEventCallback mouse_event_callback_;
+
+  bool user_input_recorded_;
+  bool callbacks_added_;
+  base::RepeatingTimer<SiteEngagementHelper> timer_;
+
 
   DISALLOW_COPY_AND_ASSIGN(SiteEngagementHelper);
 };
 
 #endif  // CHROME_BROWSER_ENGAGEMENT_SITE_ENGAGEMENT_HELPER_H_